Department of Biochemistry and Molecular Biology, UMDNJ-New Jersey Medical School, Newark, New Jersey, USA.
J Cell Physiol. 2010 Apr;223(1):224-33. doi: 10.1002/jcp.22031.
Progranulin (also known as granulin/epithelin precursor, GEP) is composed of seven granulin/epithelin repeats (granulins) and functions both as a full-length protein and as individual granulins. It is a secretory protein but a substantial amount of GEP is found inside cells, some in complexes with positive transcription elongation factor b (P-TEFb). GEP and certain granulins interact with the cyclin T1 subunit of P-TEFb, and with its HIV-1 Tat co-factor, leading to repression of transcription from the HIV promoter. We show that GEP lacking the signal peptide (GEPspm) remains inside cells and, like wild-type GEP, interacts with cyclin T1 and Tat. GEPspm represses transcription from the HIV-1 promoter at the RNA level. Granulins that bind cyclin T1 are phosphorylated by P-TEFb in vivo and in vitro on serine residues. GEPspm and those granulins that interact with cyclin T1 also inhibit transcription from cellular cad and c-myc promoters, which are highly dependent on P-TEFb, but not from the PCNA promoter. In addition, GEPspm and granulins repress transcriptional activation by VP16 or c-Myc, proteins that bind and recruit P-TEFb to responsive promoters. These data suggest that intracellular GEP is a promoter-specific transcriptional repressor that modulates the function of cellular and viral transcription factors.
颗粒蛋白前体（也称为颗粒蛋白/上皮细胞前体，GEP）由七个颗粒蛋白/上皮细胞重复序列（颗粒蛋白）组成，作为全长蛋白和单个颗粒蛋白发挥作用。它是一种分泌蛋白，但大量的 GEP 存在于细胞内，有些与正转录延伸因子 b（P-TEFb）形成复合物。GEP 和某些颗粒蛋白与 P-TEFb 的 cyclin T1 亚基以及其 HIV-1 Tat 辅助因子相互作用，导致 HIV 启动子的转录受到抑制。我们表明，缺乏信号肽的 GEP（GEPspm）仍然存在于细胞内，并且与野生型 GEP 一样与 cyclin T1 和 Tat 相互作用。GEPspm 在 RNA 水平上抑制 HIV-1 启动子的转录。体内和体外实验表明，与 cyclin T1 结合的颗粒蛋白在丝氨酸残基上被 P-TEFb 磷酸化。与 cyclin T1 相互作用的 GEPspm 和那些颗粒蛋白也抑制细胞 cad 和 c-myc 启动子的转录，这些启动子高度依赖于 P-TEFb，但不依赖于 PCNA 启动子。此外，GEPspm 和颗粒蛋白抑制 VP16 或 c-Myc 引起的转录激活，这些蛋白结合并募集 P-TEFb 到响应启动子。这些数据表明，细胞内 GEP 是一种启动子特异性转录抑制剂，可调节细胞和病毒转录因子的功能。
