FZD1 and osteosarcoma: Sp1 was previously described as a positive regulator of OB differentiation [33,50,51,52], in fact, its downregulation in a human fetal osteoblastic cell line (hFOB) resulted in reduced expression of Frizzled-1 and a decrease in ALP activity, while its overexpression increased osteosarcoma cell Saos2 mineralization [33].