ALL-TRANS-RETINOIC ACID AND HEXAMETHYLENE BISACETAMIDE (HMBA) REGULATE TGF-ALPHA AND HST-1 KFGF EXPRESSION IN DIFFERENTIATION SENSITIVE BUTNOT IN RESISTANT HUMAN TERATOCARCINOMAS/

The multipotent human teratocarcinoma (TC) cell NTera-2 clone D1 (abbr eviated NT2/D1) differentiates into a neuronal lineage after retinoic acid (RA) treatment and a distinct phenotype after hexamethylene bisac etamide (HMBA) treatment. We previously reported that RA treatment of NT2/D1 cells reduces cellular cloning efficiency and nude mouse tumori genicity. This accompanied a loss of mRNA expression of transforming g rowth factor-alpha. (TGF-alpha) and the fibroblast growth factor kFGF, also known as hst-1 (abbreviated hst-1/kFGF). This study extends prio r work by reporting that the distinct phenotype induced by HMBA also d ecreases cloning efficiency, tumorigenicity, and TGF-alpha and hst-1/k FGF mRNA expression in NT2/D1 cells. These RNA findings were confirmed by measurements of growth factor protein in the conditioned media of inducer-treated and untreated NT2/D1 cells. In two established human T C lines refractory to the actions of RA, N2102ep and Tera-1, RA fails to decrease expression of either growth factor despite induction of it s nuclear receptor, RAR-beta. However, HMBA induces morphologic matura tion and down-regulation of these growth factors in N2102ep cells. Thi s indicates that the loss of TGF-alpha and hst-1/kFGF expression serve s as a new marker of differentiation in human TCs. To explore the effe cts of these growth factors on growth and differentiation of NT2/D1 ce lls, TGF-alpha or hst-1/kFGF protein was added following inducer treat ment or no treatment. Neither growth factor blocked immunophenotypic d ifferentiation, but both promoted the growth of uninduced NT2/D1 cells in cloning assays. Growth factor expression studies were extended fro m cultured TCs to germ cell tumor biopsies, where TGF-alpha was expres sed in all and hst-1/kFGF was expressed in a subset of examined tumors . Together, these findings reveal that TGF-alpha and hst-1/kFGF are di fferentiation markers in human teratocarcinomas that appear to promote tumor cell growth without blocking differentiation.