force microscopy study arachidonic acid content membrane permeability lactate dehydrogenase release GPAT 2 subexpressing cells AFM cancer cell biology GPAT 2 expression GPAT 2 membrane damage cell surface topography GPAT 2-induced changes phenotypic differentiation marker AGPAT 11. GPAT 2 glycerol -3-phosphate acyltransferases Glycerol -3-phosphate acyltransferase 2 expression modulates cell roughness MDA-MB -231 cells