REGULATION OF PROTEIN PHOSPHATASE 2A BY CELLULAR PROTEIN

这项应用的长期目标是描述一种调节蛋白磷酸酶2A （PP2A）活性的新细胞机制，这种酶通过使这些途径中的关键蛋白去磷酸化，在调节细胞生长调节途径中起着关键作用。具体来说，我们提出一种名为HSF2的蛋白质通过结合PP2A的PR65/ a亚基来调节PP2A的活性，并通过直接与催化亚基竞争其在PR65中的结合位点来阻止其与催化亚基的结合。结果表明，阻止催化亚基结合的PR65突变与人类肺癌和结肠癌相关，从而证明了HSF2阻断PR65与催化亚基之间相互作用的能力的生物学相关性。HSF2也是调节热休克蛋白（heat shock protein, hsp）基因表达的转录因子，因此我们假设HSF2调控PP2A可能是控制热休克蛋白表达与细胞生长调控途径之间的串扰机制。为了阐明HSF2作为一种新的PP2A调节剂的功能，我们建议：1)鉴定HSF2和PR65中对这种相互作用重要的序列，2)表征调节HSF2:PR65相互作用的细胞机制，3)确定HSF2在调节细胞PP2A活性方面的功能，以及4)利用酵母双杂交相互作用筛选确定这类新型PP2A调节蛋白的其他潜在成员（我们已经用这种方法鉴定了一个新的候选蛋白d）。一种叫做mel-18的生长调节蛋白)。这些研究将通过阐明PP2A调控的新机制以及细胞中两个重要信号通路hsp调控和细胞生长/分化之间的串扰新机制来推进知识。这一知识可以帮助理解正常细胞生长调节以及癌细胞异常增殖控制。

The long-term objective of this application is to characterize what appears to be a new cellular mechanism for regulating the activity of protein phosphatase 2A (PP2A), an enzyme which plays a critical role in modulating cell growth regulatory pathways by dephosphorylating key proteins in these pathways. Specifically, we propose that a protein called HSF2 regulates PP2A activity by binding to the PR65/A subunit of PP2A and preventing its association with the catalytic subunit by directly competing with catalytic subunit for its binding site in PR65. The biological relevance of HSF2's ability to block interaction between PR65 and catalytic subunit is demonstrated by results showing that mutations in PR65 that prevent binding of catalytic subunit are associated with human lung and colon cancers. HSF2 is also known to be a transcription factor which regulates expression of heat shock protein (hsp) genes, and thus we hypothesize that HSF2 regulation of PP2A could serve as a mechanism for cross-talk between control of hsp expression and cell growth regulatory pathways. To elucidate the function of HSF2 as a novel regulator of PP2A we propose to 1) identify the sequences in HSF2 and PR65 important for this interaction, 2) characterize cellular mechanisms which regulate the HSF2:PR65 interaction, 3) determine the function of HSF2 in regulating cellular PP2A activity, and 4) identify other potential members of this new class of PP2A regulatory protein using yeast two-hybrid interaction screens (we have already identified one new candidate using this meth6d, a growth regulatory protein called mel-18). These studies will advance knowledge by elucidating a new mechanism of PP2A regulation as well as a new mechanism for cross-talk between two important signaling pathways in cells, hsp regulation and control of cell growth/differentiation. This knowledge could aid understanding of both normal cell growth regulation as well as aberrant proliferation control in cancer cells.