Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, 245 N. 15th St., MS 497, Philadelphia, PA, 19102, USA.
Cell Stress Chaperones. 2019 Nov;24(6):1127-1136. doi: 10.1007/s12192-019-01035-6. Epub 2019 Oct 22.
Developing male germ cells are extremely sensitive to heat stress; consequently, anatomic and physiologic adaptations have evolved to maintain proper thermoregulation during mammalian spermatogenesis. At the cellular level, increased expression and activity of HSP70 family members occur in response to heat stress in order to refold partially denatured proteins and restore function. In addition, several kinase-mediated signaling pathways are activated in the testis upon hyperthermia. The p38 MAP kinase (MAPK) pathway plays an important role in mitigating heat stress, and recent findings have implicated the downstream p38 substrate, MAPKAP kinase 2 (MK2), in this process. However, the precise function that this kinase plays in spermatogenesis is not completely understood. Using a proteomics-based screen, we identified and subsequently validated that the testis-enriched HSP70 family member, HspA1L, is a novel substrate of MK2. We demonstrate that MK2 phosphorylates HspA1L solely on Ser241, a residue within the N-terminal nucleotide-binding domain of the enzyme. This phosphorylation event enhances the chaperone activity of HspA1L in vitro and renders male germ cells more resistant to heat stress-induced apoptosis. Taken together, these findings illustrate a novel stress-induced signaling cascade that promotes the chaperone activity of HspA1L with implications for understanding male reproductive biology.
发育中的雄性生殖细胞对热应激极为敏感；因此，在哺乳动物精子发生过程中，已经进化出解剖和生理适应来维持适当的体温调节。在细胞水平上，热应激会导致 HSP70 家族成员的表达和活性增加，以重新折叠部分变性的蛋白质并恢复功能。此外，在睾丸内，几种激酶介导的信号通路在体温过高时被激活。p38 MAP 激酶（MAPK）途径在减轻热应激方面起着重要作用，最近的发现表明，下游的 p38 底物 MAPKAP 激酶 2（MK2）在这个过程中起作用。然而，这种激酶在精子发生中的精确作用尚不完全清楚。我们使用基于蛋白质组学的筛选方法，鉴定并随后验证了睾丸丰富的 HSP70 家族成员 HspA1L 是 MK2 的一种新型底物。我们证明 MK2 仅在 Ser241 上磷酸化 HspA1L，该残基位于酶的 N 端核苷酸结合域内。该磷酸化事件增强了 HspA1L 在体外的伴侣活性，并使雄性生殖细胞对热应激诱导的细胞凋亡更具抵抗力。总之，这些发现说明了一种新的应激诱导信号级联，该级联促进了 HspA1L 的伴侣活性，对理解男性生殖生物学具有重要意义。
