Abstract 1540: MAPK signaling profiles differ between 1,25D-sensitive HL60G and 1,25D-resistant 40AF human leukemia cells

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC The resistance to 1,25-dihydroxyvitamin D3 (1,25D) could be an obstacle for potential clinical use of vitamin D in differentiation therapy of leukemia. 40AF cells are a subline of HL60 cells and provide a model for studies of 1,25D-resistance. It is known that 40AF cells grow more rapidly than the parental cells, and have a high percentage of cells in S phase. Also, the addition of the plant antioxidant carnosic acid and a kinase inhibitor SB202190 (the combination dubbed DCS) can partially overcome the resistance to 1,25D. To better understand the basis for this resistance we examined MAPK network profiles, previously shown to be important for HL60 cell differentiation, on mRNA level by RT2-PCR arrays. The results showed that 17 out of 84 genes studied had significantly altered mRNA levels (more than 2 fold) in 40AF cells compared to HL60G cells. Eighteen genes had lower basal level of expression in 40AF compared to HL60G cells, and after partial reversal of resistance by DCS treatment these genes showed increased expression; in contrast, 20 genes had higher basal levels in 40AF cells and their expression was decreased by DCS, suggesting that these genes may be involved in 1,25D resistance. Also, DCS treatment of 40AF cells changed the expression of the RAS-ERK pathway components more obviously than the JNK and the p38MAPK pathways. Mitotic cyclins and CDKs had a generally enhanced expression in 40AF cells compared to HL60G, and their expression decreased following DCS treatment, consistent with the slow down of the cell cycle by DCS, perhaps also because several CKIs, including p21Cip1, dramatically increased. Studies using Phospho-MAPK arrays showed that treatment of both HL60G and 40AF cells with 1,25D or DCS altered the levels of phosphorylated proteins of MAPK family members P-ERK2 in the ERK pathway, P-JNK2 in the JNK pathway, P-p38 alpha/delta/gamma in the p38 pathway, P-Akt1 in the PI3/Akt pathway. The gene expression studies will be validated by Westerns, and MAPK activity by kinase assays. In summary, MAPK signaling networks may play important roles in 1,25D resistance in AML cells, and modification of network expression can influence cell cycle progression and cell differentiation to partially reverse the resistance to 1,25D of non-responding leukemia cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1540.