CDK3 and breast cancer: On the other hand, knockdown of CDK3 via two different short hairpin RNAs (shRNAs) in non-malignant breast cancer cell line MCF7 and T47D strongly reduced endogenous CDK3 expression at both mRNA and protein levels (Figure 3A and 3D), and subsequently increased cell motility and invasive ability (Figure 3B, 3C and 3E, 3F), further indicating that CDK3 plays an inhibitory role in breast cancer metastasis.