Cytoplasmic and nuclear interaction between Rb family proteins and PAI-2: a physiological crosstalk in human corneal and conjunctival epithelial cells

Abstract

Extracellular plasminogen activator inhibitor type-2 (PAI-2) is a potent inhibitor of urokinase-type plasminogen activator (u-PA) and also acts as a multifunctional protein. However, the biological activity of intracellular PAI-2, as well as its intracellular targets, until now remain an enigma. Here, we show that pRb2/p130 and Rb1/p105, but not p107, interact with PAI-2 in both the cytoplasm and nucleus of normal primary human corneal and conjunctival epithelial cells. We provided the first in vivo evidence that a specific fragment of the PAI-2 promoter is bound simultaneously by pRb2/ p130, PAI-2, E2F5, histone deacetylase 1 (HDAC1), DNA methyltransferase 1 (DNMT1), and histone methyltransferase (SUV39H1), in normal primary human corneal epithelial cells, and by pRb2/p130, PAI-2, E2F5, HDAC1, and DNMT1, in normal primary human conjunctiva epithelial cells. Our results strongly indicate a physiological interaction between pRb family members and PAI-2, suggesting the hypothesis that pRb2/p130 and PAI-2 may cooperate in modulating PAI-2 gene expression by chromatin remodeling, in normal corneal and conjunctival cells.

Rb family proteins as modulators of gene expression and new aspects regarding the interaction with chromatin remodeling enzymes

“…Recently, our studies have suggested that pRb2/p130 might be involved in mechanisms of transcriptional repression by recruiting DNMT1, HDAC1 and other chromatin remodeling enzymes (La Sala et al, 2003;Macaluso et al, 2003;Macaluso et al, 2005Macaluso et al, , 2006.…”

“…Each of the Rb family proteins binds to distinct members of the E2F transcription factors, which regulate the expression of genes whose protein products are necessary for cell proliferation and to drive cell-cycle progression (Muller et al, 2001;Young et al, 2003;Attwooll et al, 2004). More recently a broad range of studies are showing that pRb-family proteins associate with a wide variety of transcription factors and chromatin remodeling enzymes to control gene expression (La Sala et al, 2003;Macaluso et al, 2003Macaluso et al, , 2005Macaluso et al, , 2006Gunawardena et al, 2004;Parakati and DiMario, 2005).…”

“…E2F3b is expressed throughout the cell cycle and forms transcriptional repressor complexes with pRb/105 in G0 and pockets protein-independent repressor complexes in both resting and proliferating cells (Leone et al, 2000;Aslanian et al, 2004;Ginsberg, 2004). E2F4 and E2F5, which lack of a nuclear localization signal, are expressed throughout the cell cycle, but in G0 and early G1 they are bound and recruited to the nucleus by pRb2/p130 and p107 forming transcriptional repressor complexes at most of E2F-responsive promoters (Dimova and Dyson, 2005;Macaluso et al, 2005Macaluso et al, , 2006. Interestingly, it has been reported that, at some promoters, E2F1-E2F3 may bind to sites different from those vacated by E2F4 and E2F5 (Araki et al, 2003;Zhu et al, 2004;Cobrinik, 2005).…”

A Physiological Function of Inflammation-Associated SerpinB2 Is Regulation of Adaptive Immunity

“…The majority of the .860 publications listed in PubMed on SerpinB2/PAI-2 have thus assumed that the principle role of this serpin is inhibition of uPA, although a number of reports have indicated that certain activities associated with SerpinB2 expression appear unrelated to uPA inhibition (2,6,9,(11)(12)(13)(14). Although SerpinB2 can inhibit uPA in vitro, the evidence that this represents a physiological function for SerpinB2 in vivo is not compelling.…”

“…SerpinB2 has been reported to have a bewildering array of activities including regulation of monocyte and keratinocyte proliferation and differentiation (13,25,26), inhibition of apoptosis in some (5,14,27) but not other settings (28), inhibition of necrosis (29), inhibition of the IL-1b converting enzyme (30), inhibition of retinoblastoma protein degradation (31), and priming of IFN-a/b responses (6). SerpinB2 has been reported to bind annexins (32), the retinoblastoma proteins (2,12), IFN response factor 3 (33), ZNF198/FGFR1 fusion kinase (34), proteasome subunit, b type 1 (35), and vitronectin (36). These numerous activities and the limited evidence supporting a role in uPA inhibition leave no clear basis for understanding the clinical observations associated with SerpinB2.…”