passages.id: split_5_test_1710_passage
passages.type: progene_text
passages.text: It is quite likely that p16 ( INK4a ) and p14 ( ARF ) are not the pathogenetic cause of PV , but instead represent a cellular response to an abnormality of a downstream regulator of proliferation such as cyclin D , CDK4 / CDK6 , Rb , or E2F .