Retinoids have shown clinical efficacy in
cancer chemoprevention and
therapy presumably by modulating the growth, differentiation, and apoptosis of normal, premalignant, and malignant cells. To better understand the mechanisms by which
retinoids exert their effects, we used a high-throughput Western blotting method (Becton-Dickinson PowerBlot) to evaluate changes in the levels of cellular signaling
proteins in
head and neck squamous cell carcinoma cells treated with the
cytostatic all-trans-retinoic acid or with the proapoptotic
retinoids 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-
naphthalene carboxylic acid or
N-(4-hydroxyphenyl)retinamide. Treatments of the
head and neck squamous cell carcinoma cells with these
retinoids for 24 h resulted in increased levels of 14, 22, and 22
proteins and decreased levels of 5, 10, and 7
proteins, respectively. The changes in the levels of the following
proteins were confirmed by conventional western immunoblotting:
all-trans-retinoic acid increased ELF3,
topoisomerase II alpha, RB2/p130, RIG-G, and EMAPII and decreased MEF2D and
cathepsin L.
N-(4-Hydroxyphenyl)retinamide up-regulated ELF3, c-Jun, Rb2/p130, JAK1,
p67phox, Grb2,
O(6)-methylguanine-DNA methyltransferase, and Ercc-1. 6-[3-(1-Adamantyl)-4-hydroxyphenyl]-2-
naphthalene carboxylic acid increased Rb2/p130, c-Jun, Sp1, Sin, and tomosyn and decreased
cathepsin L, Mre11, and
topoisomerase II alpha. Some of these
proteins were also modulated by these
retinoids in other human
cancer cell lines. A subset of the
proteins were modulated similarly by the different
retinoids, whereas changes in other
proteins were unique for each
retinoid. These results suggest that the mechanisms by which these
retinoids modulate
proteins are distinct but may overlap. Some of the
retinoid-modulated
proteins identified in this study may be novel candidates for mediating different responses to
retinoids.