Induction of Human β-Cell Proliferation and Engraftment Using a Single G1/S Regulatory Molecule, cdk6

Abstract

OBJECTIVEMost knowledge on human β-cell cycle control derives from immunoblots of whole human islets, mixtures of β-cells and non-β-cells. We explored the presence, subcellular localization, and function of five early G1/S phase molecules—cyclins D1–3 and cdk 4 and 6—in the adult human β-cell.RESEARCH DESIGN AND METHODSImmunocytochemistry for the five molecules and their relative abilities to drive human β-cell replication were examined. Human β-cell replication, cell death, and islet function in vivo were studied in the diabetic NOD-SCID mouse.RESULTSHuman β-cells contain easily detectable cdks 4 and 6 and cyclin D3 but variable cyclin D1. Cyclin D2 was only marginally detectable. All five were principally cytoplasmic, not nuclear. Overexpression of the five, alone or in combination, led to variable increases in human β-cell replication, with the cdk6/cyclin D3 combination being the most robust (15% versus 0.3% in control β-cells). A single molecule, cdk6, proved to be capable of driving human β-cell replication in vitro and enhancing human islet engraftment/proliferation in vivo, superior to normal islets and as effectively as the combination of cdk6 plus a D-cyclin.CONCLUSIONSHuman β-cells contain abundant cdk4, cdk6, and cyclin D3, but variable amounts of cyclin D1. In contrast to rodent β-cells, they contain little or no detectable cyclin D2. They are primarily cytoplasmic and likely ineffective in basal β-cell replication. Unexpectedly, cyclin D3 and cdk6 overexpression drives human β-cell replication most effectively. Most importantly, a single molecule, cdk6, supports robust human β-cell proliferation and function in vivo.

GSK-3 inactivation or depletion promotes β-cell replication via down regulation of the CDK inhibitor, p27 (Kip1)

“…recent study has revealed that CDK6 is capable of driving human b-cell proliferation in vitro and also, it is able to increase human islet engrafment/proliferation in vivo. 35 The findings altogether indicate that inhibition of cyclin-dependent kinase (CDK) function, particularly of CDK4/6 and CDK2, via protein-protein interaction with p27 may exert a critical effect in maintaining normal adult human b-cell quiescence and thus downregulation of p27 levels in b-cells may play a key role in promoting adult human b-cell replication in vitro and in vivo. We have shown using INS-1 cells and isolated adult human islets that RNAimediated p27 depletion promotes b-cell proliferation (Fig.…”

Id3 upregulates BrdU incorporation associated with a DNA damage response, not replication, in human pancreatic β-cells

“…Recently, it was reported that overexpression of cdk-6 and cyclin D1 in isolated human β-cells in vitro induced BrdU incorporation and Ki67 expression. 35,80 It will be important to determine whether there is concomitant cell cycle completion and an increase in β-cell number as suggested by transplantation studies.…”

Targeting CDK6 in cancer: State of the art and new insights

“…CDK6 has also been found to be essential for b cell proliferation in pancreas. [12][13][14] However, CDK6 overexpression has also been shown to reduce skin tumorigenesis and cell growth in fibroblasts. 15,16 Phosphorylation of transcription factors CDK4/6 cyclin D complexes phosphorylate transcription factors, such as forkhead box M1 (FOXM1), mothers against decapentaplegic homolog 2/3 (SMAD2/3), eyes absent homolog 2 (EYA2) and methylosome protein 50 (MEP50) (cofactor) to alter their functions.…”