Kinane T B, Kang I, Chu A, Chin S H, Ercolani L
Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
Am J Physiol. 1997 Feb;272(2 Pt 2):F273-82. doi: 10.1152/ajprenal.1997.272.2.F273.
The protooncogene G alpha(i-2) plays a pivotal role in signaling pathways that control renal cell growth and differentiation. Mitogen-activated protein kinases (MAPKs) are potential downstream effectors for G alpha(i-2) in these pathways. In predifferentiated LLC-PK1 renal cells, the temporal maximal expression of G alpha(i-2) coincided with maximal activation of MAPK(p42/p44). By contrast, pertussis toxin treatment of these cells inhibited cell growth and reduced MAPK(p42/p44) activity by 30%. These findings reflected upstream activation of MAPK kinase (MEK1), as transient transfection of cells with a plasmid encoding a constitutively active form of MEK1 increased MAPK(p42/p44) activity and cell growth, whereas treatment with PD-098059, an inhibitor of MEK1 activity, reduced MAPK(p42/p44) activity and cell growth. Expression of a guanosinetriphosphatase (GTPase)-deficient G alpha(i-2) in these cells increased MAPK(p42/p44) activity and correspondingly reduced cell doubling time from 24 to 10 h without altering the activity of Raf-1 or c-Jun/stress-activated protein kinases (SAPKs). By contrast, expression of a GTPase-deficient G alpha(i-3) in these cells reduced both their cell doubling time by 30% and MAPK(p42/p44) activity by 60%. As the known MEKK isoforms (MEKK1, -2, and -3) can also activate SAPKs, these findings suggest the GTP-charged G alpha(i-2) subunit transduces growth signals in renal cells via activation of MAPK(p42/p44) and that such activation may be linked to pathways containing novel MEKK isoforms that preferentially activate MEKs.
原癌基因Gα(i - 2)在控制肾细胞生长和分化的信号通路中起关键作用。丝裂原活化蛋白激酶（MAPK）是这些通路中Gα(i - 2)潜在的下游效应器。在未分化的LLC - PK1肾细胞中，Gα(i - 2)的瞬时最大表达与MAPK（p42/p44）的最大激活同时出现。相比之下，用百日咳毒素处理这些细胞会抑制细胞生长，并使MAPK（p42/p44）活性降低30%。这些发现反映了MAPK激酶（MEK1）的上游激活，因为用编码组成型活性形式MEK1的质粒瞬时转染细胞会增加MAPK（p42/p44）活性和细胞生长，而用MEK1活性抑制剂PD - 098059处理会降低MAPK（p42/p44）活性和细胞生长。在这些细胞中表达缺乏鸟苷三磷酸酶（GTPase）的Gα(i - 2)会增加MAPK（p42/p44）活性，并相应地将细胞倍增时间从24小时缩短至10小时，而不会改变Raf - 1或c - Jun/应激激活蛋白激酶（SAPK）的活性。相比之下，在这些细胞中表达缺乏GTPase的Gα(i - 3)会使细胞倍增时间缩短30%，MAPK（p42/p44）活性降低60%。由于已知的丝裂原活化蛋白激酶激酶激酶（MEKK）同工型（MEKK1、-2和-3）也能激活SAPK，这些发现表明带GTP的Gα(i - 2)亚基通过激活MAPK（p42/p44）在肾细胞中传导生长信号，并且这种激活可能与包含优先激活MEK的新型MEKK同工型的通路有关。
