0058

INVESTIGATION OF THE MECHANISMS OF MULTIDRUG RESISTANCE CAUSED BY DIFFERENTIATION INDUCER

LI CR, FU JR, YANG J

Children Hospital of Shenzhen, Shengzhen, China

 

Objective: To investigate the regulatory mechanisms of multidrug resistance (MDR) caused by differentiation inducer.

Methods: All-trans retinoic acid and IL-4 were employed to treat human hepatoblastoma cell line (HepG2) cells. The ploliferative activity, synthesis of AFP and cell cycle distribution of the tumor cells were observed to evaluate the degree of cell differentiation. Flow cytometry and in situ hybridization were used to determine the expressing levels of p53Bcl-2, P-glycoprotein (P-gp), and c-jun and c-myc mRNA. MTT assay was used to evaluate the sensitivity of the tumor cells to chemotherapeutic agents.

Results: Both ATRA and IL-4 could induce the differentiation of HepG2 cells. ATRA treatmemt of the tumor cells led drug resistance to chemotherapies (Resistant factors:1.6~3), and IL-4 increased the sensitivity of the tumor cells to antineoplasic drugs (Reversal index:4-17). The levels of P-gp expression in ATRA-treated cells was  increased (from 54.3±8.6% up to 98.5±11.4% p<0.01),but IL-4 markedly inhibited expression of P-gp (down to 25.4%±7.3%,p<0.01). Both ATRA and IL-4 treatment could down-regulated c-jun and c-myc mRAN expression. The levels of p53 and Bcl-2 expression could be up- or down-regulated by IL-4 treatment, but were unaffected by ATRA treatment. 

Conclusion: Degree of cell differentiation and levels of c-jun and c-myc mRNA expression might not be related to alteration of drug sensitivity in inducing differentiaton of HepG2 cells with ATRA and IL-4. Increased expression of P-gp caused by ATRA might be one of factors up-regulating MDR.p53 (or Bcl-2)  might be involved in regulating sensitivity of antineoplastic drugs in inducing differentiation.

Key words: Differentiation, inducer, Multidrug resistance, P-glycoprotein    P53, Bcl-2