Undifferentiated (anaplastic) thyroid cancer (ATC) is one of the most aggressive human malignancies and no effective therapy is currently available. We show here that PPARγ levels are elevated in cells derived from ATC. Depletion of PPARγ in HTh74 ATC cells resulted in decreased cell growth, cell cycle arrest and a reduction in pRb and cyclin A and B1 levels. We further showed that both flank and orthotopic thyroid tumors derived from PPARγ-depleted cells grew more slowly than PPARγ-expressing cells. When PPARγ was overexpressed in more differentiated thyroid cancer BCPAP cells which lack PPARγ, there was increased growth and raised pRb and cyclin A and B1 levels. Finally, PPARγ depletion in ATC cells decreased their invasive capacity whereas overexpression in PTC cells increased invasiveness. These data suggest that PPARγ may play a detrimental role in thyroid cancer and that targeting it therapeutically may lead to improved treatment of advanced thyroid cancer.
