Regulation of glucose transporters by connective tissue activating peptide-III isoforms.
Connective tissue activating peptide-III (CTAP-III) is a component of platelet alpha-granules which elicits a series of responses in connective tissue cells referred to as activation, including increased glucose consumption and mitogenesis and increased secretion of hyaluronic acid and glycosaminoglycans. As anticipated by a requirement for glucose or glucose precursors in the activation process, an early event following CTAP-III activation of connective tissue cells is an increase in glucose transport. The present study investigates the molecular basis for this increase in glucose transport. Murine 3T3-F442A fibroblasts were found to respond to CTAP-III in a manner similar to human connective tissue cells (synovial cells, chondrocytes, skin fibroblasts). CTAP-III increases the rate of glucose transport to similar extents at 4 and 24 h, and at physiologic (micrograms/ml) concentrations of CTAP-III. A proteolytic cleavage product of recombinant CTAP-III (rCTAP-III-Leu-21 (des-1-15)), also known as neutrophil-activating peptide-2 (NAP-2), was found to be equally effective as CTAP-III, whereas NAP-1/interleukin-8, another member of the CTAP-III super-family, was ineffective in stimulating glucose transport. This contrasts with neutrophil chemotaxis, in which CTAP-III (des-1-15)/NAP-2 acts similarly to NAP-1/interleukin 8 while CTAP-III is ineffective. CTAP-III appears to elicit a different type of glucose transport response than many other growth factors in that its response is sustained (greater than or equal to 24 h) rather than transient (peak approximately 4 h) in confluent as well as in subconfluent cells. Western blot analysis using antibodies to the GLUT-1 glucose transporter revealed an increased level of GLUT-1 protein in response to CTAP-III isoforms that corresponded in magnitude (on a percentage basis) to the increased level of glucose transport. The increased levels of GLUT-1 protein in response to CTAP-III and rCTAP-III-Leu-21 (des-1-15)/NAP-2 were accompanied by an increase in levels of GLUT-1 mRNA of a magnitude sufficient to account for observed increased levels of GLUT-1. These results are consistent with CTAP-III isoforms stimulating glucose transport in connective tissue cells by increasing levels of GLUT-1 mRNA and is one of the few known instances in which increases in levels of GLUT-1 mRNA and protein are sufficient to account for observed increases in glucose transport. They also provide further evidence that CTAP-III (des-1-15)/NAP-2 binds to more than one type of receptor and that CTAP-III acts in a manner different than other well characterized growth factors (e.g. platelet-derived growth factor, transforming growth factor-beta) in that it causes a sustained (greater than or equal to 24 h) elevation in glucose transport in confluent as well as subconfluent cells.
Tai
P K
PK
Department of Physiology, University of Michigan Medical School, Ann Arbor 48109.
Liao
J F
JF
Hossler
P A
PA
Castor
C W
CW
Carter-Su
C
C
D016475:3T3 Cells; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001779:Blood Coagulation Factors / Q000494:pharmacology*; D003260:Contact Inhibition; D003847:Deoxyglucose / Q000378:metabolism*; D015870:Gene Expression; D066298:In Vitro Techniques; D016209:Interleukin-8 / Q000494:pharmacology; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics; D011994:Recombinant Proteins / Q000494:pharmacology; D001620:beta-Thromboglobulin
D001779:Blood Coagulation Factors; D016209:Interleukin-8; D009004:Monosaccharide Transport Proteins; C061615:PPBP protein, human; D010455:Peptides; D012333:RNA, Messenger; D011994:Recombinant Proteins; D001620:beta-Thromboglobulin; C009862:connective tissue-activating peptide; C018329:low affinity platelet factor 4; D003847:Deoxyglucose