LAPTM5 (lysosomal-associated protein transmembrane 5) is a protein that is preferentially expressed in immune cells, and it interacts with the Nedd4 family of ubiquitin ligases. Recent studies in T and B cells identified LAPTM5 as a negative regulator of T and B cell receptor levels at the plasma membrane, but a positive modulator of inflammatory signaling pathways and hence cytokine secretion in macrophages. However, the expression and function of LAPTM5 in ovarian cancer remains undefined.
LAPTM5 expression in ovarian cancer, benign and normal ovarian tissues was examined by immunohistochemistry. The LAPTM5 mRNA and protein level of OV cells were detected by Q-PCR and Western blotting respectively. Cell apoptosis, migration and invasion changes were observed through high-content screening. The proteins expression involved in epithelial-mesenchymal transition (EMT) and TGF-β mediated signaling pathways was verified by Werstern blotting and immunofluorescence. The role of LAPTM5 on tumorigenesis in vivo was detected by the xenograft model.
Our study showed that in human OV cell lines and tissues, LAPTM5 were significantly induced at both mRNA and protein levels. Furthermore, an OV cell model with downregulated LAPTM5 were established, revealing a significantly alteration of apoptosis. Moreover, analysis of the changes of migration and invasion, showed significant reduced LAPTM5 suppressed cell metastasis. Proteins involved in EMT were strongly altered, which plays a central role in cell metastasis. In addition, phosphorylated ERK1/2, p38 and JNK, key members of mitogen-activated protein kinase (MAPK) family, and phosphorylated Smad2 and Smad3 of Smad signaling pathways mediated by TGF-β regulating OV cells EMT, were strongly decreased. And, LAPTM5 knockdown also inhibited tumorigenesis in xenograft model.
Taken together, our results suggested that LAPTM 5 acts as a positive modulator of MAPK and TGFβ/Smad signaling pathways mediated by TGFβ in OV cells.
Clinical trial identification
Legal entity responsible for the study
Beijing Obstetrics and Gynecology Hospital, Capital Medical University.
The National Natural Science Foundation of China (grants 81672838), Beijing Municipal Science & Technology Commission (No. Z181100001718193).
All authors have declared no conflicts of interest.