Figure 4. Effect of cytosolic target protein transmembrane 88 (TMEM88) on proliferation and invasion of breast cancer cells.

A. Western blot analyses were utilized to assess TMEM88 protein levels after overexpression or silencing of TMEM88 in MCF-7 and MDA-MB-231 cells, respectively. Two isoforms of endogenous TMEM88 (25 kDa and 17 kDa) were detected in MCF-7 cells using an anti-TMEM88 antibody. While a Myc-tag-specific antibody failed to detect the two endogenous isoforms of TMEME88 in cells overexpressing myc-TMEM88 (TMEM88 CRA-a), two exogenous bands that were greater than 17 kDa in size were observed. We propose that the band closest to 25 kDa in size may have resulted from targeting by two tag-specific (Myc and DKK) antibodies, while the other bands may comprise post-translationally modified versions of the protein. In cells expressing the TMEM88-ΔC variant, each of these bands was smaller in size, likely due to sequence truncation. B. MTT assay analyses detected no difference in the proliferation rates of MCF-7 cells overexpressing TMEM88 or TMEM88-ΔC and MDA-MB-231 cells transfected with the TMEM88-specific siRNA. C. Average number of migrating cells that passed through the pores (counted after 16 h). Treatment with the TMEM88 siRNA resulted in a drastic reduction in the invasion rate of MDA-MB-231 cells. Overexpression of TMEM88, but not TMEM88-ΔC, resulted in marked increases in the cell invasion rates of MCF-7 cells. Values represent means ± standard errors (bars) of three independent experiments; *p < 0.05, **p < 0.01 (Student's t-test); NC, negative control.