IGF-I stimulates human intestinal smooth muscle cell growth by regulation of G1 phase cell cycle proteins.
Autocrine production of insulin-like growth factor-I (IGF-I) regulates growth of human intestinal muscle cells by activation of distinct phosphatidylinositol 3-kinase (PI3-kinase)-dependent and ERK1/2-dependent pathways. The aim of the present study was to determine the mechanisms by which IGF-I regulates the G(1) phase of the cell cycle and muscle cell proliferation. Incubation of quiescent cells with IGF-I stimulated time-dependent cell cycle progression measured by using fluorescence-activated cell sorting analysis and by incorporation of [(3)H]thymidine. Studies using a microarray-based approach were used initially to identify genes expressed in human intestinal muscle encoding proteins known to participate in the G(1) phase of the cell cycle that were regulated by IGF-I. Incubation of muscle cells for 24 h with IGF-I elicited greater than fivefold increase in the expression of cyclin D1 and greater than twofold increase in retinoblastoma protein (Rb1). IGF-I elicited a time-dependent increase in cyclin D1 protein levels mediated jointly by ERK1/2-dependent and PI3-kinase-dependent mechanisms. Increase in cyclin D1 levels was accompanied by a time-dependent increase in cyclin D1-dependent cyclin-dependent kinase-4 (CDK4) activity. IGF-I also elicited a rapid time-dependent increase in Rb-(Ser807/811) phosphorylation, the specific target of the cyclin D(1)-dependent CDK4 kinase, and a slower increase in total Rb protein levels. We conclude that IGF-I stimulates G(1) phase progression, DNA synthesis, and cell proliferation of human intestinal smooth muscle cells. Effects of IGF-I on proliferation are mediated jointly by ERK1/2-dependent and PI3-kinase-dependent pathways that regulate cyclin D1 levels, CDK4 activity, and Rb activity.
Kuemmerle
John F
JF
Department of Medicine, Medical College of Virginia Campus, Virginia Commonwealth University, PO Box 980711, Richmond, VA 23298-0711, USA. jkuemmerle@hsc.vcu.edu
Zhou
Huiping
H
Bowers
Jennifer G
JG
D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000096:biosynthesis* / Q000235:genetics; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D019938:Cyclin D1 / Q000096:biosynthesis; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis / Q000235:genetics; D005434:Flow Cytometry; D016193:G1 Phase / Q000187:drug effects* / Q000235:genetics; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007422:Intestines / Q000166:cytology / Q000187:drug effects / Q000254:growth & development*; D007583:Jejunum / Q000166:cytology / Q000254:growth & development / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000096:biosynthesis / Q000235:genetics; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000254:growth & development*; D020411:Oligonucleotide Array Sequence Analysis; D019869:Phosphatidylinositol 3-Kinases / Q000096:biosynthesis / Q000235:genetics; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger / Q000096:biosynthesis; D016160:Retinoblastoma Protein / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013268:Stimulation, Chemical; D013936:Thymidine / Q000378:metabolism
D018797:Cell Cycle Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D016160:Retinoblastoma Protein; D019938:Cyclin D1; D007334:Insulin-Like Growth Factor I; D004247:DNA; D019869:Phosphatidylinositol 3-Kinases; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases; D019950:Mitogen-Activated Protein Kinase 1; D013936:Thymidine