The mal protein, an integral component of specialized membranes, in normal cells and cancer

The MAL gene encodes a 17-kDa protein containing four putative transmembrane segments whose expression is restricted to human T cells, polarized epithelial cells and myelin-forming cells. The MAL protein has two unusual biochemical features. First, it has lipid-like properties that qualify it as a member of the group of proteolipid proteins. Second, it partitions selectively into detergent-insoluble membranes, which are known to be enriched in condensed cell membranes, consistent with MAL being distributed in highly ordered membranes in the cell. Since its original description more than thirty years ago, a large body of evidence has accumulated supporting a role of MAL in specialized membranes in all the cell types in which it is expressed. Here, we review the structure, expression and biochemical characteristics of MAL, and discuss the association of MAL with raft membranes and the function of MAL in polarized epithelial cells, T lymphocytes, and myelin-forming cells. The evidence that MAL is a putative receptor of the epsilon toxin of Clostridium perfringens, the expression of MAL in lymphomas, the hypermethylation of the MAL gene and subsequent loss of MAL expression in carcinomas are also presented. We propose a model of MAL as the organizer of specialized condensed membranes to make them functional, discuss the role of MAL as a tumor suppressor in carcinomas, consider its potential use as a cancer biomarker, and summarize the directions for future researchResearch in the laboratory of MAA was supported by a grant (PGC2018-095643-B-I00) from the Spanish Ministerio de Ciencia e Innovación (MCIN), Agencia Estatal de Investigación, and the Fondo Europeo de Desarrollo Regional, European Union (MCIN/AEI/FEDER, EU). Research in the laboratory of IC was supported by a grant (B2017/BMD-3817) from the Comunidad de Madrid, Spai

The MAL family of proteins: Normal function, expression in cancer, and potential use as cancer biomarkers

The MAL family of integral membrane proteins consists of MAL, MAL2, MALL, PLLP, CMTM8, MYADM, and MYADML2. The best characterized members are elements of the machinery that controls specialized pathways of membrane traffic and cell signaling. This review aims to help answer the following questions about the MAL-family genes: (i) is their expression regulated in cancer and, if so, how? (ii) What role do they play in cancer? (iii) Might they have biomedical applications? Analysis of large-scale gene expression datasets indicated altered levels of MAL-family transcripts in specific cancer types. A comprehensive literature search provides evidence of MAL-family gene dysregulation and protein function repurposing in cancer. For MAL, and probably for other genes of the family, dysregulation is primarily a consequence of gene methylation, although copy number alterations also contribute to varying degrees. The scrutiny of the two sources of information, datasets and published studies, reveals potential prognostic applications of MAL-family members as cancer biomarkers—for instance, MAL2 in breast cancer, MAL2 and MALL in pancreatic cancer, and MAL and MYADM in lung cancer—and other biomedical uses. The availability of validated antibodies to some MAL-family proteins sanctions their use as cancer biomarkers in routine clinical practicePID2021-123179NB-I0

MALL, a membrane-tetra-spanning proteolipid overexpressed in cancer, is present in membraneless nuclear biomolecular condensates

Proteolipids are proteins with unusual lipid-like properties. It has long been established that PLP and plasmolipin, which are two unrelated membrane-tetra-spanning myelin proteolipids, can be converted in vitro into a water-soluble form with a distinct conformation, raising the question of whether these, or other similar proteolipids, can adopt two different conformations in the cell to adapt their structure to distinct environments. Here, we show that MALL, another proteolipid with a membrane-tetra-spanning structure, distributes in membranes outside the nucleus and, within the nucleus, in membrane-less, liquid-like PML body biomolecular condensates. Detection of MALL in one or other environment was strictly dependent on the method of cell fixation used, suggesting that MALL adopts different conformations depending on its physical environment —lipidic or aqueous— in the cell. The acquisition of the condensate-compatible conformation requires PML expression. Excess MALL perturbed the distribution of the inner nuclear membrane proteins emerin and LAP2β, and that of the DNA-binding protein BAF, leading to the formation of aberrant nuclei. This effect, which is consistent with studies identifying overexpressed MALL as an unfavorable prognostic factor in cancer, could contribute to cell malignancy. Our study establishes a link between proteolipids, membranes and biomolecular condensates, with potential biomedical implication

Structure and function of the N-terminal extension of the formin INF2

In INF2—a formin linked to inherited renal and neurological disease in humans—the DID is preceded by a short N-terminal extension of unknown structure and function. INF2 activation is achieved by Ca2+-dependent association of calmodulin (CaM). Here, we show that the N-terminal extension of INF2 is organized into two α-helices, the first of which is necessary to maintain the perinuclear F-actin ring and normal cytosolic F-actin content. Biochemical assays indicated that this helix interacts directly with CaM and contains the sole CaM-binding site (CaMBS) detected in INF2. The residues W11, L14 and L18 of INF2, arranged as a 1-4-8 motif, were identified as the most important residues for the binding, W11 being the most critical of the three. This motif is conserved in vertebrate INF2 and in the human population. NMR and biochemical analyses revealed that CaM interacts directly through its C-terminal lobe with the INF2 CaMBS. Unlike control cells, INF2 KO cells lacked the perinuclear F-actin ring, had little cytosolic F-actin content, did not respond to increased Ca2+ concentrations by making more F-actin, and maintained the transcriptional cofactor MRTF predominantly in the cytoplasm. Whereas expression of intact INF2 restored all these defects, INF2 with inactivated CaMBS did not. Our study reveals the structure of the N-terminal extension, its interaction with Ca2+/CaM, and its function in INF2 activatio

Regulación de la formina INF2 normal y patogénica: papel del extremo amino terminal

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Biología Molecular. Fecha de Lectura: 20-05-2022Esta Tesis tiene embargado el acceso al texto completo hasta el 20-11-2023Las forminas constituyen una familia de quince proteínas cuya función principal es la polimerización de actina monomérica en filamentos lineales de actina (F-actina). La mutación de siete de estas forminas es la causa primaria de distintas enfermedades hereditarias. Mutaciones en la formina INF2 pueden producir dos tipos de patologías degenerativas: la glomeruloesclerosis focal y segmentaria, que es una patología renal, y la enfermedad de Charcot-Marie-Tooth, que es un trastorno neurológico que afecta a los nervios periféricos. La activación de algunas forminas es mediada por Rho GTPasas específicas que se unen a una superficie bipartita en el extremo N-terminal formada por los dominios G y DID de la formina, de forma que libera el DID de su interacción con el dominio DAD, presente en la región C-terminal. INF2 carece del dominio G y, por lo tanto, su activación parece depender de otros mecanismos reguladores. En su lugar, INF2 posee una secuencia de treinta y cinco aminoácidos que están ausentes en el resto de las forminas. En el presente trabajo hemos investigado el papel de esta secuencia en la regulación de INF2, el posible efecto de las mutaciones patogénicas en la estructura del DID y el mecanismo por el que podrían causar degeneración celular. La predicción de la estructura de la extensión N-terminal de INF2 sugiere que está organizado en dos hélices alfa. Mediante la expresión de formas de INF2 truncadas hemos establecido que la primera hélice es necesaria para el mantenimiento del contenido citoplasmático y el anillo perinuclear de F-actina de células en estado estacionario. Además, hemos encontrado que esta hélice interacciona con calmodulina en presencia de calcio, activando a INF2. La unión es dependiente del residuo W11 de INF2, siendo también importantes los residuos L14 y L18, formando juntos un motivo 1-4-8, distinto a los motivos de unión a calmodulina descritos. El aumento de los niveles de calcio intracelular produjo un mayor contenido de F-actina de una forma dependiente del sitio de unión de INF2 a calmodulina. Este cambio en el citoesqueleto de actina indujo la translocación al núcleo de MRTF, cofactor que cuando se asocia con el factor transcripcional SRF es capaz de activar la transcripción de casi un millar de genes, muchos relacionados con la citoarquitectura, contribuyendo a una extensa remodelación de la célula. Las mutaciones patogénicas de INF2 se localizan en el DID y dan lugar a variantes constitutivamente activas. Esta activación parece deberse a una alteración en la estructura del DID y no a cambios en la unión de calmodulina. La expresión de estas variantes produjo la aparición de aberraciones nucleares en células epiteliales MDCK debido a una perturbación de la mitosis, produciendo errores en la segregación cromosómica y en la formación del núcleo. La aparición progresiva de células con un fenotipo nuclear aberrante podría ser la responsable de la naturaleza degenerativa de las enfermedades asociadas a las variantes patogénicas de INF

Formins in human disease

Almost 25 years have passed since a mutation of a formin gene, DIAPH1, was identified as being responsible for a human inherited disorder: a form of sensorineural hearing loss. Since then, our knowledge of the links between formins and disease has deepened considerably. Mutations of DIAPH1 and six other formin genes (DAAM2, DIAPH2, DIAPH3, FMN2, INF2 and FHOD3) have been identified as the genetic cause of a variety of inherited human disorders, including intellectual disability, renal disease, peripheral neuropathy, thrombocytopenia, primary ovarian insuf-ficiency, hearing loss and cardiomyopathy. In addition, alterations in formin genes have been associated with a variety of pathological conditions, including developmental defects affecting the heart, nervous system and kidney, aging‐related diseases, and cancer. This review summarizes the most recent discoveries about the involvement of formin alterations in monogenic disorders and other human pathological conditions, especially cancer, with which they have been associated. In vitro results and experiments in modified animal models are discussed. Finally, we outline the directions for future research in this field.Ministerio de Ciencia e Innovación, Agencia Estatal de Investigación, and the Fondo Europeo de Desarrollo Regional, European Union (MICINN/AEI/FEDER, EU). L.L.-d.-H. was supported by a contract (FPU16/00935) from the Spanish Ministerio de Educación y Formación Profesiona

The MAL Family of Proteins: Normal Function, Expression in Cancer, and Potential Use as Cancer Biomarkers

The MAL family of integral membrane proteins consists of MAL, MAL2, MALL, PLLP, CMTM8, MYADM, and MYADML2. The best characterized members are elements of the machinery that controls specialized pathways of membrane traffic and cell signaling. This review aims to help answer the following questions about the MAL-family genes: (i) is their expression regulated in cancer and, if so, how? (ii) What role do they play in cancer? (iii) Might they have biomedical applications? Analysis of large-scale gene expression datasets indicated altered levels of MAL-family transcripts in specific cancer types. A comprehensive literature search provides evidence of MAL-family gene dysregulation and protein function repurposing in cancer. For MAL, and probably for other genes of the family, dysregulation is primarily a consequence of gene methylation, although copy number alterations also contribute to varying degrees. The scrutiny of the two sources of information, datasets and published studies, reveals potential prognostic applications of MAL-family members as cancer biomarkers—for instance, MAL2 in breast cancer, MAL2 and MALL in pancreatic cancer, and MAL and MYADM in lung cancer—and other biomedical uses. The availability of validated antibodies to some MAL-family proteins sanctions their use as cancer biomarkers in routine clinical practice

Midbody Remnant Inheritance Is Regulated by the ESCRT Subunit CHMP4C

The inheritance of the midbody remnant (MBR) breaks the symmetry of the two daughter cells, with functional consequences for lumen and primary cilium formation by polarized epithelial cells, and also for development and differentiation. However, despite its importance, neither the relationship between the plasma membrane and the inherited MBR nor the mechanism of MBR inheritance is well known. Here, the analysis by correlative light and ultra-high-resolution scanning electron microscopy reveals a membranous stalk that physically connects the MBR to the apical membrane of epithelial cells. The stalk, which derives from the uncleaved side of the midbody, concentrates the ESCRT machinery. The ESCRT CHMP4C subunit enables MBR inheritance, and its depletion dramatically reduces the percentage of ciliated cells. We demonstrate (1) that MBRs are physically connected to the plasma membrane, (2) how CHMP4C helps maintain the integrity of the connection, and (3) the functional importance of the connection.This work was supported by a grant ( PGC2018-095643-B-I00 ) to M.A.A. from the Spanish Ministerio de Ciencia e Innovación (MICIN), Agencia Estatal de Investigación , y Fondo Europeo de Desarrollo Regional , European Union ( MICIN /AEI/FEDER, UE), and by Wellcome Trust funding ( WT102871MA ) to J.M.-S. We also acknowledge the Micro and Nanofabrication Laboratory of the Instituto de Micro y Nanotecnología (MiNa), which is funded by the Comunidad de Madrid ( S2018/NMT-4291 TEC2SPACE), MICIN (project CSIC13-4E-1794 ), and EU (FEDER, FSE), for invaluable help on SEM. A contract ( FPU14/00295 ) and a short-term fellowship from EMBO to J.C.-A. are also acknowledged.Peer reviewe