Protein kinase C-zeta activation markedly enhances beta-cell proliferation: an essential role in growth factor mediated beta-cell mitogenesis.
OBJECTIVE
Diabetes results from a deficiency of functional beta-cells. Previous studies have identified hepatocyte growth factor (HGF) and parathyroid hormone-related protein (PTHrP) as two potent beta-cell mitogens. The objective of this study is to determine 1) whether HGF and PTHrP have additive/synergistic effects on beta-cell growth and proliferation; 2) the signaling pathways through which these growth factors mediate beta-cell mitogenesis; and 3) whether activation of this/these signaling pathway(s) enhances human beta-cell replication.


METHODS
We generated and phenotypically analyzed doubly transgenic mice overexpressing PTHrP and HGF in the beta-cell. INS-1 and primary mouse and human islet cells were used to identify mitogenic signaling pathways activated by HGF and/or PTHrP.


RESULTS
Combined overexpression of HGF and PTHrP in the beta-cell of doubly transgenic mice did not result in additive/synergistic effects on beta-cell growth and proliferation, suggesting potential cross-talk between signaling pathways activated by both growth factors. Examination of these signaling pathways in INS-1 cells revealed atypical protein kinase C (PKC) as a novel intracellular target activated by both HGF and PTHrP in beta-cells. Knockdown of PKC zeta, but not PKC iota/lambda, expression using specific small-interfering RNAs blocked growth factor-induced INS-1 cell proliferation. Furthermore, adenovirus-mediated delivery of kinase-dead PKC zeta completely inhibited beta-cell proliferation in primary islet cells overexpressing PTHrP and/or HGF. Finally, adenovirus-mediated delivery of constitutively active PKC zeta in mouse and human primary islet cells significantly enhanced beta-cell proliferation.


CONCLUSIONS
PKC zeta is essential for PTHrP- and HGF-induced beta-cell proliferation. PKC zeta activation could be useful in therapeutic strategies for expanding beta-cell mass in vitro and in vivo.
Vasavada
Rupangi C
RC
Department of Medicine, Division of Endocrinology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
Wang
Lin
L
Fujinaka
Yuichi
Y
Takane
Karen K
KK
Rosa
Taylor C
TC
Mellado-Gil
Jose M D
JM
Friedman
Peter A
PA
Garcia-Ocaña
Adolfo
A
D000818:Animals; D002455:Cell Division; D045744:Cell Line, Tumor; D017931:DNA Primers; D004789:Enzyme Activation; D005947:Glucose / Q000378:metabolism; D017228:Hepatocyte Growth Factor / Q000235:genetics / Q000502:physiology; D006706:Homeostasis; D006801:Humans; D050417:Insulin-Secreting Cells / Q000166:cytology* / Q000201:enzymology / Q000502:physiology*; D007340:Insulinoma; D007515:Islets of Langerhans / Q000502:physiology; D007700:Kinetics; D051379:Mice; D008822:Mice, Transgenic; D010190:Pancreatic Neoplasms; D044162:Parathyroid Hormone-Related Protein / Q000235:genetics / Q000502:physiology; D011493:Protein Kinase C / Q000378:metabolism*; D012313:RNA / Q000235:genetics; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000099221:Protein Kinase C zeta
D017931:DNA Primers; D005947:Glucose; D017228:Hepatocyte Growth Factor; D044162:Parathyroid Hormone-Related Protein; D011493:Protein Kinase C; D012313:RNA; D000099221:Protein Kinase C zeta