Background: We obtained 2 types of clones which were termed SC (sphere-shaped clone) and NSC (non-sphere-shaped clone) from 4T1 cells by monoclonal culture. SC and NSC were distinct in morphology, surface marker, metabolism and proliferation rate. With the transcriptome sequencing data analysis, we found TMED2  expressed higher in SCs. TMED2 was a member of the transmembrane emp24 domain and might play roles in cancer cell proliferation. However, its prognostic roles in breast cancer remained unknown. We aimed to investigate the prognostic values of TMED2 in patients with breast cancer.
Methods: We used UALCAN (http://ualcan.path.uab.edu) and the Human Protein Atlas (www.proteinatlas.org) to explore the TMED2 expression level and DNA methylation data between breast cancer and normal breast tissue. With Oncomine (www.oncomine.org), we investigated the copy number of TMED2  in breast cancer sample and normal breast tissue. We used the Kaplan–Meier Plotter database (http://kmplot.com/analysis) to analyze prognostic values of TMED2  mRNA expression in all breast cancers and in different intrinsic subtypes. Moreover, protein expression levels of TMED2 were confirmed by Western blot in breast cancer tissues and normal mammary tissue as well as SCs and NSCs.
Results: TMED2 significantly upregulated in breast cancer patients compared to normal mammary samples. Meanwhile, the increased expression of TMED2  mRNA was closely associated with reduced overall survival (OS) in all breast cancers, and with reduced OS in patients with ER-positive, Luminal A or Luminal B breast cancer subtypes. Moreover, western blot confirmed that TMED2 increased expressed was correlated with the reduced OS at protein levels.
Conclusion: Increased expression of TMED2 was significantly related to unfavorable outcomes in patients with breast cancer. Thus, we supposed TMED2 is oncogenic and a potential target for breast cancer therapy and these preliminary findings require further study to determine whether TMED2-targeting reagents might be developed for clinical application in breast cancer.
Keywords: breast cancer, SC, NSC, TMED2, overall survival, KM plotter