PBX1 and adrenal cortex carcinoma: As we have shown that several HOX genes correlate with proliferation markers and aggressive disease in ACC we chose to target PBX1, a transcription factor that cooperates with HOX proteins to regulate target gene expression and has been implicated in adrenal development and function.15 siRNA knockdown of PBX1 in H295R cells led to reduced levels of expression and to a marked reduction in cell proliferation (Fig. 6c, d).