CYCLIN D2 IS A MODERATELY OSCILLATING NUCLEOPROTEIN REQUIRED FOR G1 PHASE PROGRESSION IN SPECIFIC CELL-TYPES

To explore regulation and function of cyclin D2, a candidate cell cycl e-regulatory proto-oncogene, we examined subcellular localisation, cel l type- and cell cycle-dependent expression, and requirement of cyclin D2 protein for G1 progression, in a panel of 40 human normal and canc er cell types. Except for lymphoid cells and sarcoma cell lines, expre ssion of cyclin D2 was considerably more restricted than that of cycli n D1, whereas both D-type cyclin proteins were low or undetectable in cells lacking functional retinoblastoma gene product. In G1 cells, the cyclin D2 protein was more resistant to extraction and localised pred ominantly to nuclei, whereas it became more soluble and distributed in both nuclei and cytoplasm from G1/S transition onwards. Centrifugal e lutriation and multiparameter flow cytometry analyses of several cell types showed moderate cell cycle oscillation with maximum levels of th e cyclin D2 protein reached in late G1. Microinjection and/or electrop oration of antibodies to cyclin D2 during G1 arrested the cyclin D2-ex pressing lymphocytes, breast myoepithelium, and U-2-OS sarcoma cells i n G1 phase, whereas cyclin D2-negative cell types were unaffected by s uch treatment. Consistent with the putative protooncogenic role of cyc lin D2 in specific cell types, our data show that this G1 cyclin has p roperties closely resembling those of cyclin D1, including the essenti al positive role in regulation of G1.