Membrane Tension Orchestrates Rear Retraction in Matrix-Directed Cell Migration

In development, wound healing, and cancer metastasis, vertebrate cells move through 3D interstitial matrix, responding to chemical and physical guidance cues. Protrusion at the cell front has been extensively studied, but the retraction phase of the migration cycle is not well understood. Here, we show that fast-moving cells guided by matrix cues establish positive feedback control of rear retraction by sensing membrane tension. We reveal a mechanism of rear retraction in 3D matrix and durotaxis controlled by caveolae, which form in response to low membrane tension at the cell rear. Caveolae activate RhoA-ROCK1/PKN2 signaling via the RhoA guanidine nucleotide exchange factor (GEF) Ect2 to control local F-actin organization and contractility in this subcellular region and promote translocation of the cell rear. A positive feedback loop between cytoskeletal signaling and membrane tension leads to rapid retraction to complete the migration cycle in fast-moving cells, providing directional memory to drive persistent cell migration in complex matrices. © 2019 The AuthorsCell migration through 3D matrix is critical to developmental and disease processes, but the mechanisms that control rear retraction are poorly understood. Hetmanski et al. show that differential membrane tension allows caveolae to form at the rear of migrating cells and activate the contractile actin cytoskeleton to promote rapid retraction. © 2019 The Author

Mutant p53 regulates dicer through p63-dependent and -independent mechanisms to promote an invasive phenotype

The control and processing of microRNAs (miRs) is critical in the regulation of all cellular responses. Previous studies have suggested that a reduction in the expression of certain miRs, or an overall decrease in miR processing through the partial depletion of Dicer, can promote enhanced metastatic potential. We show here that Dicer depletion can promote the invasive behavior of cells that is reflected in enhanced recycling and activation of the growth factor receptors Met and EGF receptor. These responses are also seen in response to the expression of tumor-derived mutant p53s, and we show that mutant p53 can down-regulate Dicer expression through both direct inhibition of the TAp63-mediated transcriptional activation of Dicer and a TAp63-independent control of Dicer protein expression. Our results delineate a clear relationship between mutant p53, TAp63, and Dicer that might contribute to the metastatic function of mutant p53 but, interestingly, also reveal TAp63-independent functions of mutant p53 in controlling Dicer activity

Rab11 and Its Effector Rab Coupling Protein Contribute to the Trafficking of beta 1 Integrins during Axon Growth in Adult Dorsal Root Ganglion Neurons and PC12 Cells

Integrins play an important part in axon growth, but integrin traffic in neurons is poorly understood. Expression of the tenascin-C-binding integrin alpha 9 promotes axon regeneration. We have therefore studied the mechanism by which alpha 9 integrin and its partner beta 1 are trafficked along axons and at the growth cone using adult DRG neurons and PC12 cells. We have focused on the small GTPase Rab11 and its effector Rab coupling protein (RCP), as they are involved in the long-range trafficking of beta 1 integrins in other cells. Rab11 colocalizes with alpha 9 and other alpha integrins and with beta 1 integrin in growth cones and axons, and immunopurified Rab11 vesicles contain alpha 9 and beta 1. Endocytosed beta 1 integrins traffic via Rab11. However, Rab11 vesicles in axons are generally static, and alpha 9 integrins undergo bouts of movement during which they leave the Rab11 compartment. In growth cones, alpha 9 and beta 1 overlap with RCP, particularly at the growth cone periphery. We show that beta 1 integrin trafficking during neurite outgrowth involves Rab11 and RCP, and that manipulation of these molecules alters surface integrin levels and axon growth, and can be used to enhance alpha 9 integrin-dependent neurite outgrowth. Our data suggest that manipulation of trafficking via Rab11 and RCP could be a useful strategy for promoting integrin-dependent axonal regeneration

Mutant p53 Drives Invasion by Promoting Integrin Recycling

p53 is a tumor suppressor protein whose function is frequently lost in cancers through missense mutations within the Tp53 gene. This results in the expression of point-mutated p53 proteins that have both lost wild-type tumor suppressor activity and show gain of functions that contribute to transformation and metastasis. Here, we show that mutant p53 expression can promote invasion, loss of directionality of migration, and metastatic behavior. These activities of p53 reflect enhanced integrin and epidermal growth factor receptor (EGFR) trafficking, which depends on Rab-coupling protein (RCP) and results in constitutive activation of EGFR/integrin signaling. We provide evidence that mutant p53 promotes cell invasion via the inhibition of TAp63, and simultaneous loss of p53 and TAp63 recapitulates the phenotype of mutant p53 in cells. These findings open the possibility that blocking alpha5/beta1-integrin and/or the EGF receptor will have therapeutic benefit in mutant p53-expressing cancers

Epigenetic inactivation of protein kinase D1 in gastric cancer and its role in gastric cancer cell migration and invasion

Protein kinase D (PKD) 1 influences cell migration by mediating both trans-Golgi vesicle fission and integrin recycling to the cell surface. Using restriction landmark genomic scanning methods, we found that the promoter region of PKD1 was aberrantly methylated in gastric cancer cell lines. Silencing of PKD1 expression was detected in 72.7% of gastric cancer cell lines examined, and the silencing was associated with CpG hypermethylation in the promoter region of PKD1. Treatment with 5-aza-2'-deoxycytidine and trichostatin A partially reversed PKD1 methylation and restored gene expression in PKD1-silenced cell lines. Real-time reverse transcription-polymerase chain reaction analysis of 96 paired clinical primary gastric cancer samples revealed that 59% of the analyzed tumors had a > 2-fold decrease in PKD1 expression compared with each normal-appearing tissue and that this downregulation of PKD1 expression was significantly correlated with increased methylation. We also observed a gradual increase in the level of promoter methylation of PKD1 in aging, normal-appearing mucosal tissues, suggesting that PKD1 methylation may be one of the earliest events that predispose an individual to gastric cancer. PKD1 expression was required for directional migration of gastric cancer cells. Furthermore, knock down of PKD1 by RNA interference promoted the invasiveness of cell lines that expressed PKD1 at relatively high levels. Based on these results, we propose that PKD1 is frequently silenced by epigenetic regulation, which plays a role in cell migration and metastasis in gastric cancer

Multisite Assessment of Aging-Related Tau Astrogliopathy (ARTAG).

Aging-related tau astrogliopathy (ARTAG) is a recently introduced terminology. To facilitate the consistent identification of ARTAG and to distinguish it from astroglial tau pathologies observed in the primary frontotemporal lobar degeneration tauopathies we evaluated how consistently neuropathologists recognize (1) different astroglial tau immunoreactivities, including those of ARTAG and those associated with primary tauopathies (Study 1); (2) ARTAG types (Study 2A); and (3) ARTAG severity (Study 2B). Microphotographs and scanned sections immunostained for phosphorylated tau (AT8) were made available for download and preview. Percentage of agreement and kappa values with 95% confidence interval (CI) were calculated for each evaluation. The overall agreement for Study 1 was >60% with a kappa value of 0.55 (95% CI 0.433-0.645). Moderate agreement (>90%, kappa 0.48, 95% CI 0.457-0.900) was reached in Study 2A for the identification of ARTAG pathology for each ARTAG subtype (kappa 0.37-0.72), whereas fair agreement (kappa 0.40, 95% CI 0.341-0.445) was reached for the evaluation of ARTAG severity. The overall assessment of ARTAG showed moderate agreement (kappa 0.60, 95% CI 0.534-0.653) among raters. Our study supports the application of the current harmonized evaluation strategy for ARTAG with a slight modification of the evaluation of its severity

Extracellular matrix and its role in spermatogenesis

In adult mammalian testes, such as rats, Sertoli and germ cells at different stages of their development in the seminiferous epithelium are in close contact with the basement membrane, a modified form of extracellular matrix (ECM). In essence, Sertoli and germ cells in particular spermatogonia are “resting” on the basement membrane at different stages of the seminiferous epithelial cycle, relying on its structural and hormonal supports. Thus, it is not entirely unexpected that ECM plays a significant role in regulating spermatogenesis, particularly spermatogonia and Sertoli cells, and the blood-testis barrier (BTB) constituted by Sertoli cells since these cells are in physical contact with the basement membrane. Additionally, the basement membrane is also in close contact with the underlying collagen network and the myoid cell layers, which together with the lymphatic network, constitute the tunica propria. The seminiferous epithelium and the tunica propria, in turn, constitute the seminiferous tubule, which is the functional unit that produces spermatozoa via its interaction with Leydig cells in the interstitium. In short, the basement membrane and the underlying collagen network that create the acellular zone of the tunica propria may even facilitate cross-talk between the seminiferous epithelium, the myoid cells and cells in the interstitium. Recent studies in the field have illustrated the crucial role of ECM in supporting Sertoli and germ cell function in the seminiferous epithelium, including the BTB dynamics. In this chapter, we summarize some of the latest findings in the field regarding the functional role of ECM in spermatogenesis using the adult rat testis as a model. We also high light specific areas of research that deserve attention for investigators in the field

Extracellular Matrix and Its Role in Spermatogenesis

In adult mammalian testes, such as rats, Sertoli and germ cells at different stages of their development in the seminiferous epithelium are in close contact with the basement membrane, a modified form of extracellular matrix (ECM). In essence, Sertoli and germ cells in particular spermatogonia are “resting” on the basement membrane at different stages of the seminiferous epithelial cycle, relying on its structural and hormonal supports. Thus, it is not entirely unexpected that ECM plays a significant role in regulating spermatogenesis, particularly spermatogonia and Sertoli cells, and the blood-testis barrier (BTB) constituted by Sertoli cells since these cells are in physical contact with the basement membrane. Additionally, the basement membrane is also in close contact with the underlying collagen network and the myoid cell layers, which together with the lymphatic network, constitute the tunica propria. The seminiferous epithelium and the tunica propria, in turn, constitute the seminiferous tubule, which is the functional unit that produces spermatozoa via its interaction with Leydig cells in the interstitium. In short, the basement membrane and the underlying collagen network that create the acellular zone of the tunica propria may even facilitate cross-talk between the seminiferous epithelium, the myoid cells and cells in the interstitium. Recent studies in the field have illustrated the crucial role of ECM in supporting Sertoli and germ cell function in the seminiferous epithelium, including the BTB dynamics. In this chapter, we summarize some of the latest findings in the field regarding the functional role of ECM in spermatogenesis using the adult rat testis as a model. We also highlight specific areas of research that deserve attention for investigators in the field