The G protein G alpha(13) is required for growth factor-induced cell migration.

Heterotrimeric G proteins are critical cellular signal transducers. They are known to directly relay signals from seven-transmembrane G protein-coupled receptors (GPCRs) to downstream effectors. On the other hand, receptor tyrosine kinases (RTKs), a different family of membrane receptors, signal through docking sites in their carboxy-terminal tails created by autophosphorylated tyrosine residues. Here we show that a heterotrimeric G protein, G alpha(13), is essential for RTK-induced migration of mouse fibroblast and endothelial cells. G alpha(13) activity in cell migration is retained in a C-terminal mutant that is defective in GPCR coupling, suggesting that the migration function is independent of GPCR signaling. Thus, G alpha(13) appears to be a critical signal transducer for RTKs as well as GPCRs. This broader role of G alpha(13) in cell migration initiated by two types of receptors could provide a molecular basis for the vascular system defects exhibited by G alpha(13) knockout mice.

Hyplip2, a new gene for combined hyperlipidemia and increased atherosclerosis.

OBJECTIVE: We previously reported the mapping of a quantitative trait locus (QTL) on chromosome 15 contributing to hyperlipidemia in a cross between inbred strains MRL/MpJ (MRL) and BALB/cJ (BALB). Using marker-assisted breeding, we constructed a congenic strain in which chromosome 15 interval from MRL is placed on the genetic background of BALB. The congenic allowed us to confirm the QTL result and to further characterize the properties and location of the underlying gene. METHODS AND RESULTS: On chow and high-fat (atherogenic) diets, the congenic mice exhibited higher levels of plasma triglycerides and cholesterol than BALB mice. In response to the atherogenic diet, the congenic mice but not BALB mice exhibited a dramatic approximately 30-fold increase in atherogenic lesions accompanied by approximately 2-fold decrease in high-density lipoprotein cholesterol levels. With respect to atherosclerotic lesions and some lipid parameters, this chromosome 15 gene, designated Hyplip2, exhibited dominant inheritance. Expression array analyses suggested that Hyplip2 may influence inflammatory and bile acid synthesis pathways. Finally, we demonstrated the usefulness of subcongenic strains to narrow the locus (50 Mbp) with the goal of positionally cloning Hyplip2. CONCLUSIONS: Our data demonstrate that the Hyplip2 gene significantly contributes to combined hyperlipidemia and increased atherosclerosis in mice.

Regulation of hematopoietic-specific G-protein Galpha15 and Galpha16 by protein kinase C.

Heterotrimeric G proteins mediate cell growth and differentiation by coupling cell surface receptors to intracellular effector enzymes. The G-protein alpha subunit, Galpha(16), and its murine homologue Galpha(15), are expressed specifically in hematopoietic cells and their expression is highly regulated during differentiation of normal and leukemic cells. In this study, we examined the phosphorylation of Galpha(15)/Galpha(16) and its role in receptor and effector coupling. We observed a PMA-stimulated intact cell phosphorylation of Galpha(15) in COS7 cells transfected with Galpha(15) and protein kinase Calpha (PKCalpha), and phosphorylation of endogenous Galpha(16) in HL60 cells. We also showed that peptides derived from the two G-proteins were phosphorylated in vitro using purified brain PKC. Furthermore, we identified the putative phosphorylation site and showed that mutation or deletion of this PKC phosphorylation site inhibited phospholipase C (PLC) activation. The behavior of double mutants with the constitutively active G-protein mutation (QL-mutant) and mutation in the putative phosphorylation site suggests that the phosphorylation site of Galpha(15/16) is essential for receptor-coupled activation of PLC, but not for direct interaction of the G-protein with PLC-beta.

Interaction of G alpha(12) with G alpha(13) and G alpha(q) signaling pathways.

The G(12) subfamily of heterotrimeric G-proteins consists of two members, G(12) and G(13). Gene-targeting studies have revealed a role for G(13) in blood vessel development. Mice lacking the alpha subunit of G(13) die around embryonic day 10 as the result of an angiogenic defect. On the other hand, the physiological role of G(12) is still unclear. To address this issue, we generated G alpha(12)-deficient mice. In contrast to the G alpha(13)-deficient mice, G alpha(12)-deficient mice are viable, fertile, and do not show apparent abnormalities. However, G alpha(12) does not seem to be entirely redundant, because in the offspring generated from G alpha(12)+/- G alpha(13)+/- intercrosses, at least one intact G alpha(12) allele is required for the survival of animals with only one G alpha(13) allele. In addition, G alpha(12) and G alpha(13) showed a difference in mediating cell migratory response to lysophosphatidic acid in embryonic fibroblast cells. Furthermore, mice lacking both G alpha(12) and G alpha(q) die in utero at about embryonic day 13. These data indicate that the G alpha(12)-mediated signaling pathway functionally interacts not only with the G alpha(13)- but also with the G alpha(q/11)-mediated signaling systems.