Western blot analysis. Procedures for protein extraction, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and immunoblotting have been described in detail.⁶  The polyclonal anti-cyclin D1 and anti-β-tubulin antibodies, sc-718 and sc-9104, respectively, were purchased from Santa Cruz Biotechnology (Santa Cruz, CA). The lower bands observed are due to a cross-reactivity shown by anti-cyclin D1 antibody against cyclin D2.