HSG cells differentiated by culture on extracellular matrix involves induction of S-adenosylmethione decarboxylase and ornithine decarboxylase.

The human salivary gland (HSG) epithelial cell line can differentiate when cultured on extracellular matrix preparations. We previously identified >30 genes upregulated by adhesion of HSG cells to extracellular matrix. In the current studies, we examined the role of one of these genes, the polyamine pathway biosynthetic enzyme S-adenosylmethionine decarboxylase (SAM-DC) and the related enzyme, ornithine decarboxylase (ODC), on HSG cell differentiation during culture on extracellular matrix. HSG cells cultured on fibronectin-, collagen I gel-, and Matrigel-coated substrates for 12-24 h upregulated SAM-DC and ODC mRNA expression and enzyme activity compared to cells cultured on non-precoated substrates. After 3-5 days, HSG cells grown on Matrigel- or collagen I gel-coated substrates acquired a differentiated phenotype: the cells showed changes in culture morphology and increased expression of salivary gland differentiation markers (vimentin, SN-cystatin, and alpha-amylase). Further, culturing the cells on substrates precoated with an anti-beta1-integrin-antibody promoted differentiation-like changes. HSG cells cultured on collagen I- or Matrigel-coated substrates rapidly entered the cell cycle but showed decreased cell proliferation at longer times. In contrast, cell proliferation was enhanced on fibronectin-coated substrates compared to cells on non-precoated substrates. Treatment with the polyamine synthesis inhibitors, difluoromethylornithine (DFMO), and methylglyoxal bis-(guanylhydrazone) (MGBG), inhibited cell proliferation and delayed (3)H-thymidine incorporation in HSG cells cultured on all of the substrates. Further, inclusion of DFMO and MGBG inhibited or delayed acquisition of the differentiated phenotype in HSG cells cultured on Matrigel- or collagen I gel-coated substrates. This suggests that the adhesion-dependent expression of SAM-DC and ODC contributes to extracellular matrix-dependent HSG cell differentiation.