CDKN1B and breast cancer: This together with enhanced expression of Cdkn1a and Cdkn1b in melanoma and breast cancer cell lines depleted of endogenous Tbx2 [12], [13], [17] (and this study), indicates that Tbx3 and the closely related Tbx2 protein occupy DNA sites in the Cdkn1a and Cdkn1b loci in other cell types and may regulate these genes in other developmental contexts as well.