Diaz Francisco Mendez, Godinez David Sanchez, Solano Francisco, Jasani Akshi, Alcaide Maria, Kellogg Douglas R
Department of Molecular, Cell and Developmental Biology University of California, Santa Cruz.
bioRxiv. 2024 Nov 21:2024.11.20.624605. doi: 10.1101/2024.11.20.624605.
Cell cycle progression is dependent upon cell growth. Cells must therefore translate growth into a proportional signal that can be used to determine when there has been sufficient growth for cell cycle progression. In budding yeast, the protein kinase Gin4 is required for normal control of cell growth and undergoes gradual hyperphosphorylation and activation that are dependent upon growth and proportional to the extent of growth, which suggests that Gin4 could function in mechanisms that measure cell growth. However, the molecular mechanisms that drive hyperphosphorylation of Gin4 are poorly understood. Here, we used biochemical reconstitution and genetic analysis to test hypotheses for the mechanisms that drive phosphorylation of Gin4. We ruled out a previous model in which phosphatidylserine delivered to sites of plasma membrane growth binds Gin4 to initiate autophosphorylation. Instead, we show that Elm1, a homolog of the mammalian Lkb1 tumor suppressor kinase, is sufficient to promote hyperphosphorylation of Gin4 in vitro, likely via initiation of Gin4 autophosphorylation. Furthermore, we show that casein kinase I is required for growth-dependent hyperphosphorylation of Gin4 and also for normal regulation of Elm1. Together, these discoveries lead to new insight into mechanisms that link cell cycle progression to cell growth.
细胞周期进程依赖于细胞生长。因此，细胞必须将生长转化为一种成比例的信号，该信号可用于确定何时细胞生长足以推动细胞周期进程。在芽殖酵母中，蛋白激酶Gin4是正常控制细胞生长所必需的，它会经历逐渐的过度磷酸化和激活，这依赖于生长且与生长程度成比例，这表明Gin4可能在测量细胞生长的机制中发挥作用。然而，驱动Gin4过度磷酸化的分子机制却知之甚少。在这里，我们使用生化重建和遗传分析来检验驱动Gin4磷酸化机制的假设。我们排除了先前的一个模型，即转运到质膜生长位点的磷脂酰丝氨酸结合Gin4以启动自磷酸化。相反，我们发现哺乳动物Lkb1肿瘤抑制激酶的同源物Elm1足以在体外促进Gin4的过度磷酸化，可能是通过启动Gin4的自磷酸化。此外，我们表明酪蛋白激酶I是Gin4生长依赖性过度磷酸化所必需的，也是Elm1正常调控所必需的。这些发现共同为将细胞周期进程与细胞生长联系起来的机制带来了新的见解。
