Sphingosine Kinases in Cancer Cell Signaling

Sphingosine kinase （SphK）是调节sphingosin -1-磷酸（S1P）水平的中心酶，S1P是一种生物活性鞘脂代谢物，也是5种S1P受体家族的配体。我们之前已经克隆并鉴定了2种不同的异构体SphK1和SphK2。SphK1被多种刺激激活，促进细胞增殖、细胞存活、迁移和肿瘤形成。SphK1和细胞内生成的S1P可以“由内向外”发出信号，调节细胞骨架重排和细胞运动，但独立于S1P受体刺激细胞生长和抑制细胞凋亡。值得注意的是，尽管与SphK1序列高度相似，并且拥有相同的5个保守结构域，但我们最近发现SphK2不仅促进生长和存活，而且抑制生长并促进凋亡。本提案的目标是确定这两种非常密切相关且相似的同工酶如何产生相同的产物却具有如此不同的功能。我们将检验SphK1和SphK2的相反作用是由于它们的特定调控和/或易位到不同的细胞区室，从而产生不同的S1P或其他具有独特功能的磷酸化鞘基，从而影响对转化表型特别重要的细胞过程。将利用生化和遗传学方法来确定内源性SphK1和SphK2在癌细胞的生长、存活和运动中是否具有冗余、重叠、互补或拮抗功能。我们还将阐明它们在调节神经酰胺生物合成和鞘脂组中的未被认识的作用，并确定SphK2是否是连接Bcl-2家族、钙稳态和细胞凋亡调节的双功能BH3-only蛋白。总的来说，这些研究将为SphK1和SphK2的生理作用增加一个新的维度，SphK1和SphK2的活性在控制S1P水平方面是中心和必需的，S1P是一种有效的脂质介质，调节许多对癌症重要的细胞过程。

DESCRIPTION (provided by applicant): Sphingosine kinase (SphK) is a central enzyme regulating the levels of sphingosine-1-phosphate (S1P), a bioactive sphingolipid metabolite and a ligand for a family of 5 S1P receptors. We have previously cloned and characterized 2 distinct isoforms, SphK1 and SphK2. SphK1 is activated by a numerous stimuli to promote cell proliferation, cell survival, migration and tumor formation. SphK1 and intracellularly generated S1P can signal "inside-out" to regulate cytoskeletal rearrangements and cell movement, yet stimulates cell growth and suppresses apoptosis independently of S1P receptors. Remarkably, although highly similar in sequence to SphK1 and possessing the same 5 conserved domains, we recently found that SphK2 rather than promoting growth and survival, suppressed growth and also enhanced apoptosis. The goal of this proposal is to determine how these 2 very closely related and similar isoenzymes that can produce the same product can have such different functions. We will examine the hypothesis that the opposite actions of SphK1 and SphK2 result from their specific regulation and/or translocation to distinct cellular compartments to produce distinct pools of S1P or other phosphorylated sphingoid bases that have unique functions, and thus affect cellular processes that are particularly important for the transformed phenotype. Biochemical and genetic approaches will be utilized to determine whether endogenous SphK1 and SphK2 have redundant, overlapping, complementary, or antagonistic functions in growth, survival and motility of cancer cells. We will also elucidate their unrecognized roles in regulating ceramide biosynthesis and the sphingolipidome and determine whether SphK2 is a dual function BH3-only protein that links the Bcl-2 family, calcium homeostasis, and regulation of apoptosis. Collectively, these studies will add a new dimension to the physiological roles of SphK1 and SphK2 whose activities are central and obligatory in controlling levels of S1P, a potent lipid mediator that regulates many cellular processes important for cancer.