BackgroundTumor cells benefit from their ability to avoid apoptosis and invade other tissues. The endoplasmic reticulum (ER) membrane protein Sec62 is a key player in these processes. Sec62 is essential for cell migration and protects tumor cells against thapsigargin-induced ER stress, which are both linked to cytosolic Ca2+. SEC62 silencing leads to elevated cytosolic Ca2+ and increased ER Ca2+ leakage after thapsigargin treatment. Sec62 protein levels are significantly increased in different tumors, including prostate, lung and thyroid cancer.MethodsIn lung cancer, the influence of Sec62 protein levels on patient survival was analyzed using the Kaplan-Meier method and log-rank test. To elucidate the underlying pathophysiological functions of Sec62, Ca2+ imaging techniques, real-time cell analysis and cell migration assays were performed. The effects of treatment with the calmodulin antagonists, trifluoperazine (TFP) and ophiobolin A, on cellular Ca2+ homeostasis, cell growth and cell migration were compared with the effects of siRNA-mediated Sec62 depletion or the expression of a mutated SEC62 variant in vitro. Using Biacore analysis we examined the Ca2+-sensitive interaction of Sec62 with the Sec61 complex.ResultsSec62 overproduction significantly correlated with reduced patient survival. Therefore, Sec62 is not only a predictive marker for this type of tumor, but also an interesting therapeutic target. The present study suggests a regulatory function for Sec62 in the major Ca2+ leakage channel in the ER, Sec61, by a direct and Ca2+-sensitive interaction. A Ca2+-binding motif in Sec62 is essential for its molecular function. Treatment of cells with calmodulin antagonists mimicked Sec62 depletion by inhibiting cell migration and rendering the cells sensitive to thapsigargin treatment.ConclusionsTargeting tumors that overproduce Sec62 with calmodulin antagonists in combination with targeted thapsigargin analogues may offer novel personalized therapeutic options.

The heterotrimeric Sec61 complex and the dimeric Sec62/Sec63 complex are located in the membrane of the human endoplasmic reticulum (ER) and play a central role in translocation of nascent and newly synthesized precursor polypeptides into the ER. This process involves targeting of the precursors to the membrane and opening of the polypeptide conducting Sec61 channel for translocation. Apart from this central role in the intracellular transport of polypeptides, several studies of the last decade uncovered additional functions of Sec proteins in intracellular signaling: Sec62 can induce ER-phagy in the process of recovery of cells from ER stress and the Sec61 channel can also act as a passive ER calcium leak channel. Furthermore, mutations, amplifications and an overexpression of the SEC genes were linked to various diseases including kidney and liver diseases, diabetes and human cancer. Studies of the last decade could not only elucidate the functional role of Sec proteins in the pathogenesis of these diseases, but also demonstrate a relevance of Sec62 as a prognostic and predictive biomarker in head and neck cancer, prostate and lung cancer including a basis for new therapeutic strategies. In this article, we review the current understanding of protein transport across the ER membrane as central function of Sec proteins and further focus on recent studies that gave first insights into the functional role and therapeutic relevance of Sec61, Sec62 and Sec63 in human diseases.

The molecular carcinogenesis of lung cancer has yet to be clearly elucidated. We investigated the possible oncogenic function of SEC62 in lung cancer, which was predicted based on our previous findings that lung and thyroid cancer tissue samples exhibited increased Sec62 protein levels. The SEC62 gene locus is at 3q26.2, and 3q amplification is reportedly the most common genomic alteration in non-small cell lung cancer. We analyzed SEC62 mRNA and protein levels in tissue samples from lung cancer patients by real-time quantitative PCR, Western blot, and IHC and found significantly increased SEC62 mRNA and protein levels in tumors compared with tumor-free tissue samples from the same patients. Correlation analyses revealed significantly higher Sec62 levels in tumors with lymph node metastases compared with nonmetastatic tumors, as well as in poorly compared with moderately differentiated tumors. On the basis of these promising results, we examined the role of Sec62 in cancer cell biology in vitro. Cell migration assays with lung and thyroid cancer cells showed distinct stimulation of migration in SEC62-overexpressing cells and inhibition of migration in Sec62-depleted cells. Moreover, we found that SEC62 silencing sensitized the cells to thapsigargin-induced endoplasmic reticulum stress. Thus, our results indicate that SEC62 represents a potential candidate oncogene in the amplified 3q region in cases of non-small cell lung cancer and harbors various functions in cancer cell biology.

In this study, we characterize the immune microenvironment and neoantigen landscape of salivary gland cancers using RNA sequencing in 76 tumors representing the 3 most lethal histologies: adenoid cystic carcinoma (ACC), myoepithelial carcinoma (MECA), and salivary duct carcinoma (SDC). We show that SDCs exhibited high levels of immune infiltration, with corresponding higher levels of T cell dysfunction, and higher mutational load. ACCs were characterized by an immuneexcluded microenvironment, the presence of M2-polarized macrophages and myeloidderived suppressor cells, and very low mutational load. MECAs were more heterogeneous, with both immune-low and immune-high phenotypes. Across all SGCs, immune infiltration was associated with mutation-and fusion-derived neoantigens. These findings provide new insights into the immune microenvironment and neoantigen landscape of SGCs, showing that mechanisms of immune escape differ by histology. These data nominate potential immunologic vulnerabilities and may help guide the next steps of investigation in precision immunotherapy for these difficult-to-treat cancers. Research.

Chromosome 3q26 amplification represents a frequent alteration in head and neck squamous cell carcinomas (HNSCCs). Overexpression of 3q26 encoded genes SEC62 and SOX2 was detected in various cancers, including HNSCCs, indicating their potential function as oncogenes. In our study, we elucidated the function of SEC62 and SOX2 in HNSCC patients, with a main focus on their effect on lymphatic metastasis and patient survival. We analyzed SEC62 and SOX2 expression in tissue specimens from 65 HNSCC patients and 29 patients with cervical cancer of unknown primary (CUP); a higher SEC62 and lower SOX2 expression was observed in the lymph node metastases from HNSCC patients compared with the respective primary tumor. Lymph node metastases from CUP patients showed higher SEC62 and lower SOX2 expression compared with lymph node metastases from HNSCC patients. When proceeding from the N1 to the N3 stage, SEC62 expression in the lymph node metastases showed an increase and SOX2 expression showed a decrease. Moreover, both genes showed a highly significant relevance as prognostic biomarkers, with the worst prognosis for patients with high SEC62 and low SOX2 expression levels. In functional analyses, knockdown of SEC62 resulted in an inhibition of HNSCC cell migration while, conversely, SEC62 and SOX2 overexpression stimulated cell migration. Taken together, our study showed that the expression of the 3q oncogenes SEC62 and SOX2 affects lymphatic metastasis and cell migration in HNSCC and CUP patients and has a high prognostic relevance in these diseases.

BackgroundChromosome 3 amplification affecting the 3q26 region is a common genomic alteration in cervical cancer, typically marking the transition of precancerous intraepithelial lesions to an invasive phenotype. Though potential 3q encoded target genes of this amplification have been identified, a functional correlation of potential oncogenic function is still missing. In this study, we investigated copy number changes and the expression level of SEC62 encoded at 3q26.2 as a new potential 3q oncogene in dysplastic cervical lesions and analyzed its role in cervical cancer cell biology.MethodsExpression levels of Sec62 and vimentin were analyzed in liquid based cytology specimens from 107 women with varying grades of cervical dysplasia ranging from normal cases to cancer by immunofluorescence cytology. Additionally, a subset of 20 representative cases was used for FISH analyses targeting SEC62. To further explore the functional role of Sec62 in cervical cancer, HeLa cells were transfected with a SEC62 plasmid or SEC62 siRNA and analyzed for their proliferation and migration potential using real-time monitoring and trans-well systems as well as changes in the expression of EMT markers.ResultsFISH analyses of the swabbed cells showed a rising number of SEC62 gains and amplifications correlating to the grade of dysplasia with the highest incidence in high grade squamous intraepithelial lesions and squamous cell carcinomas. When analyzing the expression level of Sec62 and vimentin, we found a gradually increasing expression level of both proteins according to the severity of the dysplasia. In functional analyses, SEC62 silencing inhibited and SEC62 overexpression stimulated the migration of HeLa cells with only marginal effects on cell proliferation, the expression level of EMT markers and the cytoskeleton structure.ConclusionsOur study suggests SEC62 as a target gene of 3q26 amplification and a stimulator of cellular migration in dysplastic cervical lesions. Hence, SEC62 could serve as a potential marker for 3q amplification, providing useful information about the dignity and biology of dysplastic cervical lesions.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-016-2739-6) contains supplementary material, which is available to authorized users.

The rough endoplasmic reticulum (ER) of nucleated human cells has crucial functions in protein biogenesis, calcium (Ca2+) homeostasis, and signal transduction. Among the roughly one hundred components, which are involved in protein import and protein folding or assembly, two components stand out: The Sec61 complex and BiP. The Sec61 complex in the ER membrane represents the major entry point for precursor polypeptides into the membrane or lumen of the ER and provides a conduit for Ca2+ ions from the ER lumen to the cytosol. The second component, the Hsp70-type molecular chaperone immunoglobulin heavy chain binding protein, short BiP, plays central roles in protein folding and assembly (hence its name), protein import, cellular Ca2+ homeostasis, and various intracellular signal transduction pathways. For the purpose of this review, we focus on these two components, their relevant allosteric effectors and on the question of how their respective functional cycles are linked in order to reconcile the apparently contradictory features of the ER membrane, selective permeability for precursor polypeptides, and impermeability for Ca2+. The key issues are that the Sec61 complex exists in two conformations: An open and a closed state that are in a dynamic equilibrium with each other, and that BiP contributes to its gating in both directions in cooperation with different co-chaperones. While the open Sec61 complex forms an aqueous polypeptide-conducting- and transiently Ca2+-permeable channel, the closed complex is impermeable even to Ca2+. Therefore, we discuss the human hereditary and tumor diseases that are linked to Sec61 channel gating, termed Sec61-channelopathies, as disturbances of selective polypeptide-impermeability and/or aberrant Ca2+-permeability.

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