Formation of Heterochromatin and Cellular Senescence Driven by HIRA and ASF 1a

大多数正常人类细胞经历有限数量的细胞分裂，最终进入不可逆转的 停滞状态，通过衰老或分化。这两个过程都对 人类健康；它们之间会影响出生缺陷、癌症和人类衰老的退化效应。 例如，胚胎发育过程中细胞分化的缺陷会导致人类出生缺陷。 衰老和分化程序都以染色质的深刻变化为特征 结构，在这两种情况下，这被认为是导致细胞表型改变的原因。我们正在使用 衰老作为模型系统来研究这些染色质结构的变化及其对两个 衰老和终末分化的特征，抑制增殖促进基因和 细胞周期退出。 最近，我们发现染色质调节蛋白HIRA及其物理结合伙伴ASF1a， 两者在衰老细胞中一种新的染色质结构的形成中起着关键作用，这种结构被称为衰老 相关异染色质灶(SAHF)。SAHF被认为可以抑制驱动细胞增殖的基因。平拉 和ASF1a驱动SAHF的形成，与一个亚核细胞器，即PML机构协同作用；以及两个 染色质相关蛋白、HP1和宏H_2A。初步数据表明，Hira/ASF1a途径 被关键的增殖调节激酶GSK3激活。为了理解生理学意义 和SAHF形成的分子基础及其在早衰细胞中的激活方式，我们将使用细胞和 分子生物学技术可以： 具体目的1.研究SaHF的结构及其与Hira/ASF1a和PML的组装机制 并确定其关键的生长抑制组分。 特定目的2.研究染色质相关蛋白掺入SAHF的功能和机制 蛋白质、HP1和宏H_2A。 具体目的3.研究GSK3活性在Hira对PML小体定位中的作用 SAHF和衰老的开始。

Most normal human cells undergo a limited number of cell divisions, eventually entering an irreversibly arrested state, through either senescence or differentiation. Both processes have major implications for human health; between them impacting birth defects, cancer and the degenerative effects of human aging. For example, defects in cell differentiation during embryo development result in human birth defects. Senescence and differentiation programs are both characterized by profound changes in chromatin structure, and, in both cases, this is thought to contribute to the altered cell phenotype. We are using senescence as a model system to study these changes in chromatin structure and their contribution to two hallmarks of both senescence and terminal differentiation, repression of proliferation-promoting genes and cell cycle exit. Recently, we showed that the chromatin regulatory protein, HIRA, and its physical binding partner, ASF1a, both play a key role in formation of a novel chromatin structure in senescent cells, called senescence associated heterochromatin foci (SAHF). SAHF is thought to silence genes that drive cell proliferation. HIRA and ASF1a drive SAHF formation, acting in concert with a subnuclear organelle, the PML body; and two chromatin associated proteins, HP1 and macroH2A. Preliminary data indicate that the HIRA/ASF1a pathway is activated by the key proliferation-regulating kinase, GSK3. To understand the physiological significance and molecular basis of SAHF formation and its mode of activation in presenescent cells, we will use cell and molecular biology techniques to: Specific Aim 1. Investigate the structure of SAHF, its mechanism of assembly by HIRA/ASF1a and PML nuclear bodies and identify its key growth suppressor components. Specific Aim 2. Investigate the function and mechanism of incorporation into SAHF of chromatin associated proteins, HP1 and macroH2A. Specific Aim 3. Investigate the role of GSK3 activity in localization of HIRA to PML bodies, formation of SAHF and onset of senescence.