Bishop L, Dimaline R, Blackmore C, Deavall D, Dockray G J, Varro A
Physiological Laboratory, University of Liverpool, Liverpool, England.
Gastroenterology. 1998 Nov;115(5):1154-62. doi: 10.1016/s0016-5085(98)70086-1.
BACKGROUND & AIMS: Amidated gastrins are acid secretagogues and growth factors. Their precursor, progastrin, is a growth factor but not a secretagogue. Cleavage of progastrin at Arg94/95 determines the expression of these two alternative patterns of biological activity. We examined the hypothesis that cleavage at Arg94/95 is regulated by phosphorylation of the adjacent Ser96 residue.
Hamster insulinoma cells were stably transfected with wild-type rat preprogastrin and phosphorylation site mutants; biosynthesis was studied by a pulse-chase protocol.
Rates of cleavage at Arg94/95 were increased in Ser96-->Ala compared with wild-type progastrin. Mutation of Glu98 to Ala inhibited incorporation of [32P]phosphate into progastrin and increased the rate of cleavage at Arg94/95. Conversely, mutation of Ser96 to Asp reduced rates of cleavage at Arg94/95. Depletion of calcium stores decreased phosphorylation of Ser96 and increased cleavage at Arg94/95. Modulation of Ser96 phosphorylation also directly influenced the ratio of progastrin-cleavage products (progastrin/CFP; G17Gly/G34Gly) secreted into the medium.
Phosphorylation of progastrin is dependent on calcium stores, determines prohormone cleavage rates, and thereby controls the production of the alternative active products of preprogastrin translation.
酰胺化胃泌素是胃酸分泌刺激物和生长因子。其前体，即前胃泌素，是一种生长因子，但不是胃酸分泌刺激物。前胃泌素在精氨酸94/95处的切割决定了这两种生物活性替代模式的表达。我们检验了精氨酸94/95处的切割受相邻丝氨酸96残基磷酸化调节这一假说。
用野生型大鼠前前胃泌素和磷酸化位点突变体稳定转染仓鼠胰岛素瘤细胞；通过脉冲追踪实验研究生物合成。
与野生型前胃泌素相比，丝氨酸96突变为丙氨酸时，精氨酸94/95处的切割速率增加。谷氨酸98突变为丙氨酸抑制了[32P]磷酸盐掺入前胃泌素，并增加了精氨酸94/95处的切割速率。相反，丝氨酸96突变为天冬氨酸降低了精氨酸94/95处的切割速率。钙库耗竭降低了丝氨酸96的磷酸化水平，并增加了精氨酸94/95处的切割。丝氨酸96磷酸化的调节也直接影响分泌到培养基中的前胃泌素切割产物（前胃泌素/CFP；G17Gly/G34Gly）的比例。
前胃泌素的磷酸化依赖于钙库，决定激素原切割速率，从而控制前前胃泌素翻译的替代活性产物的产生。
