The Human MDM2 Oncoprotein Increases the Transcriptional Activity and the Protein Level of the p53 Homolog p63

Genetic alteration of the p53 tumor suppressor gene, which monitors DNA damage and operates cell cycle checkpoints, is a major factor in the development of human malignancies. The p53 protein belongs to a family that also includes two structurally related proteins, p63 and p73. Although all three proteins share similar transcriptional functions and antiproliferative effects, each of them appears to play a distinct role in development and tumor suppression. One of the principal regulators of p53 activity is the MDM2 protein. The interaction of MDM2 with p53 inhibits p53 transcriptional activity and targets p53 for ubiquitin-dependent degradation. The ability of MDM2 to inhibit p53 functions is antagonized by the ARF oncosuppressor protein. We show here that like p53, the p63alpha and p63gamma isoforms are able to associate with human MDM2 (HDM2). Overexpression of HDM2 increased the steady-state level of intracellular p63 and enhanced its transcriptional activity. Both effects appeared to be counteracted by ARF coexpression. These data indicate that p63 can be activated by HDM2 under conditions in which p53 is inhibited. Therefore, HDM2 expression could support p63-specific transcriptional functions on a common set of genes, keeping interference by p53 at a minimum

Pancreatic Progenitor Commitment Is Marked by an Increase in Ink4a/Arf Expression

The identification of the molecular mechanisms controlling early cell fate decisions in mammals is of paramount importance as the ability to determine specific lineage differentiation represents a significant opportunity for new therapies. Pancreatic Progenitor Cells (PPCs) constitute a regenerative reserve essential for the maintenance and regeneration of the pancreas. Besides, PPCs represent an excellent model for understanding pathological pancreatic cellular remodeling. Given the lack of valid markers of early endoderm, the identification of new ones is of fundamental importance. Both products of the Ink4a/Arf locus, in addition to being critical cell-cycle regulators, appear to be involved in several disease pathologies. Moreover, the locus’ expression is epigenetically regulated in ES reprogramming processes, thus constituting the ideal candidates to modulate PPCs homeostasis. In this study, starting from mouse embryonic stem cells (mESCs), we analyzed the early stages of pancreatic commitment. By inducing mESCs commitment to the pancreatic lineage, we observed that both products of the Cdkn2a locus, Ink4a and Arf, mark a naïve pancreatic cellular state that resembled PPC-like specification. Treatment with epi-drugs suggests a role for chromatin remodeling in the CDKN2a (Cycline Dependent Kinase Inhibitor 2A) locus regulation in line with previous observations in other cellular systems. Our data considerably improve the comprehension of pancreatic cellular ontogeny, which could be critical for implementing pluripotent stem cells programming and reprogramming toward pancreatic lineage commitment

The Hay Wells Syndrome-Derived TAp63aQ540L Mutant has Impaired Transcriptional and Cell Growth Regulatory Activity

p63 mutations have been associated with several human hereditary disorders characterized by ectodermal dysplasia such as EEC (ectrodactyly, ectodermal dysplasia, clefting) syndrome, ADULT (acro, dermato, ungual, lacrimal, tooth) syndrome and AEC (ankyloblepharon, ectodermal dysplasia, clefting) syndrome (also called Hay-Wells syndrome). The location and functional effects of the mutations that underlie these syndromes reveal a striking genotype-phenotype correlation. Unlike EEC and ADULT that result from missense mutations in the DNA-binding domain of p63, AEC is solely caused by missense mutations in the SAM domain of p63. In this paper we report a study on the TAp63alpha isoform, the first to be expressed during development of the embryonic epithelia, and on its naturally occurring Q540L mutant derived from an AEC patient. To assess the effects of the Q540L mutation, we generated stable cell lines expressing TAp63alpha wt, DeltaNp63alpha or the TAp63alpha-Q540L mutant protein and used them to systematically compare the cell growth regulatory activity of the mutant and wt p63 proteins and to generate, by microarray analysis, a comprehensive profile of differential gene expression. We found that the Q540L substitution impairs thetranscriptional activity of TAp63alpha and causes misregulation of genes involved in the control of cell growth and epidermal differentiation

A Regulatory Mechanism Involving TBP-1/Tat-Binding Protein 1 and Akt/PKB in the Control of Cell Proliferation

TBP-1 /Tat-Binding Protein 1 (also named Rpt-5, S6a or PSMC3) is a multifunctional protein, originally identified as a regulator of HIV-1-Tat mediated transcription. It is an AAA-ATPase component of the 19S regulative subunit of the proteasome and, as other members of this protein family, fulfils different cellular functions including proteolysis and transcriptional regulation. We and others reported that over expression of TBP-1 diminishes cell proliferation in different cellular contexts with mechanisms yet to be defined. Accordingly, we demonstrated that TBP-1 binds to and stabilizes the p14ARF oncosuppressor increasing its anti-oncogenic functions. However, TBP-1 restrains cell proliferation also in the absence of ARF, raising the question of what are the molecular pathways involved. Herein we demonstrate that stable knock-down of TBP-1 in human immortalized fibroblasts increases cell proliferation, migration and resistance to apoptosis induced by serum deprivation. We observe that TBP-1 silencing causes activation of the Akt/PKB kinase and that in turn TBP-1, itself, is a downstream target of Akt/PKB. Moreover, MDM2, a known Akt target, plays a major role in this regulation. Altogether, our data suggest the existence of a negative feedback loop involving Akt/PKB that might act as a sensor to modulate TBP-1 levels in proliferating cells

IN "POLPO ... SITION" E ALTRI BREVI RACCONTI

Assalito dalla felicità corsi al mare, guardai l’acqua e fui preso da una forza, non mia, non umana che mi trascinò in acqua. Lì venni rapito da fantastiche sensazioni, l’adrenalina salì a mille, vidi un enorme creatura che suscitò in me delle emozioni mai provate prima, si era avvicinata talmente tanto che stava per toccarmi e, appena lo fece, il mio corpo si illuminò magicamente, le mie mani iniziarono pian piano ad assottigliarsi, il mio petto diventava sempre più piccolo e tondo e da lì a poco, ero diventato un polpo

An intriguing association between the p14ARF oncosuppressor and TBP-1, a multifunctional protein with a potential role in the control of cell growth

Gli studi condotti hanno avuto lo scopo di chiarire il potenziale ruolo oncosoprressivo di TBP-1, una proteina multifunzionale, che fa parte del complesso regolativo 26S del proteasoma, indagando, in primis, sul significato funzionale dell'associazione tra p14ARF, un oncosoppressore umano e TBP-1. I risultati hanno indicato che TPB-1 protegge p14ARF dall'azione degradativa del proteasoma. Inoltre si è cercato di decifrare il pathway molecolare attraverso cui TBP-1 esercita un effetto antiproliferativo , indipendentemente da p14ARF. Questa parte del lavoro ha portato all'identificazione di PKB/Akt quale uno dei partners funzionali di TBP-1

Analysis of the p63 function in cell proliferation and differentiation through the study of the mechanisms regulating p63 protein stability and transcriptional activity.

caratterizzazione funzionale e molecolare del fattore trascrizionale p63 nelle sue isoforme selvatiche e mutanti nonché sulla comprensione degli effetti esercitati sullo stesso dall’overespressione di due proteine: il soppressore tumorale p14 ARF ed il fattore trascrizionale DLX3. In particolare gli studi condotti hanno avuto lo scopo di comprendere il meccanismo molecolare attraverso il quale il soppressore tumorale p14 ARF inibisce l’attività trascrizionale di p63 e comprendere il meccanismo secondo il quale l’overespressione di DLX3, fattore trascrizionale implicato nel differenziamento epiteliale, regola i livelli di espressione di p63

Transcriptional regulation of the human tumor suppressor p14ARF by E2F1, E2F2, E2F3 and SP1-like factors

The human ARF/INK4a locus encodes two cell cycle inhibitors, p16INK4a and p14ARF, by using separate promoters. A variety of mitogenic stimuli upregulate ARF but a direct modulation at the transcriptional level has been reported only for E2F-1. We show here that the ARF promoter is strongly responsive also to E2F2 and E2F3, thus providing a strong support to their suggested role in the induction of apoptosis. Through the usage of both deletion mutants and/or site-directed mutants, we surprisingly found that none of the four putative E2F consensus sites is strictly necessary for the upregulation of ARF expression, as a minimal deletion mutant, lacking all the putative E2F binding sites, is still transactivated by E2F. Moreover, our data suggest that the ARF promoter is regulated by E2F through both direct binding to the promoter sequences and indirectly, probably by Sp1-like factors