Heteroarotinoids elevate tissue transglutaminase in human erythroleukemia cells

Abstract

Tissue transglutaminase (tTg) is postulated to play a role in apoptosis and/or differentiation in cultured cells. All trans‐retinoic acid (RA) is a naturally occurring molecule that binds to retinoic acid receptors responsible for apoptosis and differentiation. RA induces tTg activity in human erythroleukemia (HEL) cells, but in general, results in high toxicity. Heteroarotinoids (Hets) are less toxic synthetic structural analogues of RA and are defined as systems with one aromatic ring and one heteroatom (N, S, or O). We propose that Hets have a role in differentiation and/or apoptosis of HEL cells. To test this, HEL cells were cultured for 48 h with RA (tTg induction), DMSO (negative control) and Hets 1, 2, and 4 (experimental compounds). Hets 1, 2 and 4 showed significant growth inhibitions, lowered cell viability and induced apoptosis relative to DMSO and RA. tTg was quantitated in HEL cells using an inhibition ELISA assay. When an anti‐tTg monoclonal antibody was added to a sample containing tTg, an antigen‐antibody complex was formed. When this sample was added to a 96‐well microtiter plate containing attached tTg, less color was produced relative to an antibody sample that was not premixed with tTg. Preliminary results in Het 2 and Het 4‐treated cells showed elevated levels of tTg. The results appear promising for our hypothesis of a role for Hets in differentiation and/or apoptosis of HEL cells.