THE ROLE OF SQMI PROTEIN IN METHOTREXATE TRANSPORT AND SENSITIVITY OF HUMAN CARCINOMAS
- Quezon City FEU-NRMF April 1997
- 197 pages
ABSTRACT: The levels of a novel membrane protein, SQMI, has been found to correlate with sensitivity of uncloned aquamous carcinoma cell lines to methotrexate (MTX) (Bernal et. al., 1990). This dissertation research was done to identify the mechanism of MTX resistence correlated with SQMI protein levels and to understand the role of SQMI protein in MTX sensitivity. Primary cultures and uncloned cell lines of various lung carcinoma cell types show a correlation of MTX sensitivity with SQMI protein levels and MTX transpoert indicating a possible role of SQMI protein in MTX sentivity by increased MTX transport SQMI protein levels also correlated with the degree of differentiation of the lung cancer cell type. In bronchial epithelial cells induced toward squamous differentiation, SQMI protein was transiently induced during early stages of squamous differentiation of NBE cells concomitant with increased MTX sensitivity. MTX resistent cloned cell lines were developed in order to pin point the mechanism of resistance that correlates with SQMI protein levels. MTX resistant sublines developed from a clonally derived SqCHN cell line, SCC15S1, showed high correlation of SQMI protein expression with MTX transport but not with other mechanism of MTX resistence such as MTX-polyglutamylation and DHFR enzyme activity. Exposure of MTX resistent SCC15R1.3 to SQMI protein in the media led to increased MTX sensitivity and transport. Exposure of MTX resistant cells to liposomes containing SQM1 protein also increased MTX uptake and sensitivity. Transfection of SQM1 cDNA in a mammalian expression vector, p205, again increased MTX uptake and sensitivity of CEM lymphoblastic lymphoma cells and MTX resistant SCC1R1.3.