Regulation of glucose homeostasis by KSR1 and MARK2.
Protein scaffolds control the intensity and duration of signaling and dictate the specificity of signaling through MAP kinase pathways. KSR1 is a molecular scaffold of the Raf/MEK/ERK MAP kinase cascade that regulates the intensity and duration of ERK activation. Relative to wild-type mice, ksr1⁻/⁻ mice are modestly glucose intolerant, but show a normal response to exogenous insulin. However, ksr1⁻/⁻ mice also demonstrate a three-fold increase in serum insulin levels in response to a glucose challenge, suggesting a role for KSR1 in insulin secretion. The kinase MARK2 is closely related to C-TAK1, a known regulator of KSR1. Mice lacking MARK2 have an increased rate of glucose disposal in response to exogenous insulin, increased glucose tolerance, and are resistant to diet-induced obesity. mark2⁻/⁻ksr1⁻/⁻ (DKO) mice were compared to wild type, mark2⁻/⁻, and ksr1⁻/⁻ mice for their ability to regulate glucose homeostasis. Here we show that disruption of KSR1 in mark2⁻/⁻ mice reverses the increased sensitivity to exogenous insulin resulting from MARK2 deletion. DKO mice respond to exogenous insulin similarly to wild type and ksr1⁻/⁻ mice. These data suggest a model whereby MARK2 negatively regulates insulin sensitivity in peripheral tissue through inhibition of KSR1. Consistent with this model, we found that MARK2 binds and phosphorylates KSR1 on Ser392. Phosphorylation of Ser392 is a critical regulator of KSR1 stability, subcellular location, and ERK activation. These data reveal an unexpected role for the molecular scaffold KSR1 in insulin-regulated glucose metabolism.
Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, Nebraska, United States of America.
Paula J
PJ
Klutho
Diane L
DL
Costanzo-Garvey
Robert E
RE
Lewis
D000818:Animals; D018797:Cell Cycle Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D055786:Gene Knockout Techniques; D005947:Glucose / Q000378:metabolism*; D057809:HEK293 Cells; D006706:Homeostasis; D006801:Humans; D007328:Insulin / Q000097:blood / Q000378:metabolism; D000078790:Insulin Secretion; D051379:Mice; D010766:Phosphorylation; D011494:Protein Kinases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
D018797:Cell Cycle Proteins; D007328:Insulin; D011494:Protein Kinases; C097199:KSR-1 protein kinase; C122043:Mark2 protein, mouse; D017346:Protein Serine-Threonine Kinases; D005947:Glucose