SEC62 Protein Research Articles

The endoplasmic reticulum membrane protein Sec62 as potential therapeutic target in SEC62 overexpressing tumors.

The human SEC62 gene is located on chromosome 3q, was characterized as a tumor driver gene and is found to be overexpressed in an ever-growing number of tumors, particularly those with 3q26 amplification. Where analyzed, SEC62 overexpression was associated with poor prognosis. Sec62 protein is a membrane protein of the endoplasmic reticulum (ER) and has functions in endoplasmic reticulum protein import, endoplasmic reticulum-phagy and -in cooperation with the cytosolic protein calmodulin- the maintenance of cellular calcium homeostasis. Various human tumors show SEC62 overexpression in immunohistochemistry and corresponding cell lines confirm this phenomenon in western blots and immunofluorescence. Furthermore, these tumor cells are characterized by increased stress tolerance and migratory as well as invasive potential, three hallmarks of cancer cells. Strikingly, plasmid-driven overexpression of SEC62 in non-SEC62 overexpressing cells introduces the same three hallmarks of cancer into the transfected cells. Depletion of Sec62 from either type of SEC62 overexpressing tumor cells by treatment with SEC62-targeting siRNAs leads to reduced stress tolerance and reduced migratory as well as invasive potential. Where tested, treatment of SEC62 overexpressing tumor cells with the small molecule/calmodulin antagonist trifluoperazine (TFP) phenocopied the effect of SEC62-targeting siRNAs. Recently, first phase II clinical trials with the prodrug mipsagargin/G202, which targets cellular calcium homeostasis in prostate cells as well as neovascular tissue in various tumors were started. According to experiments with tumor cell lines, however, SEC62 overexpressing tumor cells may be less responsive or resistant against such treatment. Therefore, murine tumor models for tumor growth or metastasis were evaluated with respect to their responsiveness to treatment with a mipsagargin analog (thapsigargin), or trifluoperazine, which had previously been in clinical use for the treatment of schizophrenia, or with the combination of both drugs. So far, no additive effect of the two drugs was observed but trifluoperazine had an inhibitory effect on tumor growth and metastatic potential in the models. Here, we review the state of affairs.

Role of the SEC62 gene in dermato-oncology - impact on tumor cell biology, prognostication, and personalized therapy management.

The SEC62 gene encodes for a transmembrane protein of the endoplasmic reticulum (ER). Sec62 protein is involved in the post-translational transport of secretory and membrane-bound proteins in eukaryotic cells, regulates intracellular calcium homeostasis through direct interaction with the Sec61 channel and makes a decisive contribution to the cellular compensation of ER stress in the context of recovER-phagy. A significantly increased expression of the SEC62 gene has already been demonstrated in various tumor entities. First approaches of a targeted therapy have been tested for various tumor entities in vitro and in vivo with promising results that motivate further preclinical and clinical studies. Nevertheless, many questions remain unanswered, in particular with regard to the molecular mechanisms underlying the observed clinical effects, and require further investigation in future studies. The protein also plays a relevant role in dermato-oncology. The overexpression of SEC62 in atypical fibroxanthomas and malignant melanomas has already been demonstrated and a correlation of SEC62 expression with various clinical and pathological features has been observed. Future studies, especially in vivo and clinical, will show whether Sec62 can be established as a prognostic marker in dermato-oncology and whether it can serve as a starting point for targeted therapy.

Antagonizing Sec62 function in intracellular Ca2+ homeostasis represents a novel therapeutic strategy for head and neck cancer.

Various cancer types including head and neck squamous cell carcinomas (HNSCC) show a frequent amplification of chromosomal region 3q26 that encodes, among others, for the SEC62 gene. Located in the ER membrane, this translocation protein is known to play a critical role as a potential driver oncogene in cancer development. High SEC62 expression levels were observed in various cancer entities and were associated with a poor outcome and increased metastatic burden. Because of its intracellular localization the SEC62 protein is poorly accessible for therapeutic antibodies, therefore a functional SEC62 knockdown represents the most promising mechanism of a potential antineoplastic targeted therapy. By stimulating the Ca2+ efflux from the ER lumen and thereby increasing cellular stress levels, a functional inhibition of SEC62 bears the potential to limit tumor growth and metastasis formation. In this study, two potential anti-metastatic and -proliferative agents that counteract SEC62 function were investigated in functional in vitro assays by utilizing an immortalized human hypopharyngeal cancer cell line as well as a newly established orthotopic murine in vivo model. Additionally, a CRISPR/Cas9 based SEC62 knockout HNSCC cell line was generated and functionally characterized for its relevance in HNSCC cell proliferation and migration as well as sensitivity to SEC62 targeted therapy in vitro.

Abstract P4-06-06: Role of lymphatic SEC62 expression in prediction of treatment response in patients undergoing neoadjuvant chemotherapy for primary breast cancer

Abstract Background Chromosome 3q26 amplifications have been shown to represent a frequent alteration in various cancer entities including breast cancer. SEC62 - a 3q26 encoded gene - was identified as a potential onco- and tumor-driver gene for the pathogenesis of breast cancer. Sec62 seems to induce an increased stress tolerance, enhanced cell migration and proliferation in SEC62 overexpressing cells. Patients with SEC62 overexpressing breast cancer have been shown to have a higher rate of lymph node metastasis and poorer overall prognosis. Hence, we aspired to further evaluate the function of lymphatic SEC62 expression and its predictive role on the response to neoadjuvant chemotherapy. Objectives We aimed to assess the role of lymph node SEC62 expression as a predictive biomarker for response to neoadjuvant chemotherapy, besides we sought to evaluate potential differences in SEC62 expression levels in metastatic lymph node core biopsies and final pathology specimen according to breast cancer subtype. Material & Methods All nodal positive patients treated for primary breast cancer with neoadjuvant chemotherapy at the Department of Gynaecology and Obstetricts, Saarland University Hospital, Homburg, Germany between 01/2009 and 12/2019 were enrolled in this retrospective study. We analyzed SEC62 expression in tissue samples by immunohistochemistry (IHC). Sec62 immunoreactivity was evaluated using the immunoreactive score (IRS) according to Remmele and Stegner (0-12). For the assessment of the Sec62 protein content of the tumor cells, we rated Sec62 “low” for a score of 0-8, and “high” for 9-12 as described in previous publications. IHC was performed on initial lymph node core biopsy (CB) tissue (pre-treatment) or sentinel node biopsy specimen and on definite pathology specimen (PS) obtained during axillary dissection after completion of neoadjuvant chemotherapy.SEC62 expressions in both samples were compared and correlated with response to neoadjuvant chemotherapy, evaluated pathologically using the semi-quantitative response to neoadjuvant chemotherapy scoring system by Sinn et al. ranging from 0 (no effect) to 4 (no tumor detectable). Results 103 patients were assessed for eligibility. 15 cases were excluded, due to incomplete clinical information or insufficient slide quality, leaving 88 patients for final analysis. Median patient age was 55 (32-78) years and median response to neoadjuvant chemotherapy score of 2 (0-4). 11 (12.5%) patients had luminal A, 31 (35.2%) luminal B, 21 (23.9%) Her2/neu positive and 25 (28.4%) triple negative breast cancer. Median SEC62 expression in lymph node core biopsies was significantly higher compared to expression in final specimen (p<0.01). While no differences in basic expression of SEC62 in CB and the response to neoadjuvant chemotherapy were detected, patients with an IRS score ≤ 8 in PS and patients with a difference of IRS score ≥6 between CB and PS showed a significantly higher median response to neoadjuvant chemotherapy score compared to other patients (p< 0.01). Analyzing median Sec62 IHC expression in final pathology specimen, we observed significantly lower Sec62 scores for Her2/neu positive and triple negative patients compared to other subtypes (p<0.01). Median SEC62 expression showed the highest decrease between CB and PS in Her2/neu positive and triple negative patients. Regarding response to neoadjuvant chemotherapy, the effects described above could be observed in all breast cancer subtypes, but were strongest in triple negative patients. Conclusion We identified lymph node SEC62 expression as a promising biomarker for prediction of response to neoadjuvant chemotherapy in breast cancer patients. This effect seems to be strongest in patients with triple negative breast cancer. Citation Format: Julia Zimmermann, Anna Jung, Merle Doerk, Mariz Kasoha, Barbara Linxweiler, Maximilian Linxweiler, Mathias Wagner, Rainer Bohle, Marc Radosa, Erich Solomayer, Julia C Radosa. Role of lymphatic SEC62 expression in prediction of treatment response in patients undergoing neoadjuvant chemotherapy for primary breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-06-06.

Globular adiponectin alleviates chronic intermittent hypoxia-induced H9C2 cardiomyocytes apoptosis via ER-phagy induction

ABSTRACT This study evaluated the effects of endoplasmic reticulum autophagy (ER-phagy) and globular adiponectin (gAPN) on chronic intermittent hypoxia (CIH)-induced H9C2 cardiomyocytes injury while investigating potential mechanisms of action. The CIH model of H9C2 cardiomyocytes was established in this study. CCK-8 assay was used to determine cell viability post-exposure to various CIH times and gAPN concentrations. Flow cytometry was used to observe H9C2 cardiomyocytes apoptosis and immunofluorescence was used to measure ER-phagy and SEC62 activation. Western blot was used to observe ER stress and AMPK pathway. Results indicated that ER stress was activated in H9C2 cardiomyocytes exposed to CIH. Inhibition of ER stress reduced CIH-induced cell apoptosis. gAPN attenuated CIH-induced ER stress and H9C2 cardiomyocytes apoptosis. ER-phagy and SEC62 protein level were induced by CIH, while gAPN highly enhanced these changes. Inhibition of SEC62 expression reduced ER-phagy and increased ER stress and H9C2 cardiomyocytes apoptosis. Moreover, gAPN induced AMPK expression. Inhibition of AMPK expression reduced SEC62-mediated ER-phagy and increased the H9C2 cardiomyocytes apoptosis. Altogether, our study suggested that gAPN upregulated SEC62-mediated ER-phagy to extenuate ER stress, and mitigated H9C2 cardiomyocytes apoptosis induced by CIH through AMPK activation.

Abstract P1-10-28: Role of Sec62 in prediction of response to neoadjuvant chemotherapy in patients with primary breast cancer

Abstract Background Chromosome 3q26 amplifications have been shown to represent a frequent alteration in various cancer entities including breast cancer. SEC62 - a 3q26 encoded gene - was identified as a potential oncogene and tumor-driver-gene for the pathogenesis of breast cancer. Although the precise physiological function of the respective protein Sec62 is not completely understood, it is hypothesized, that Sec62 induces an increased stress tolerance and enhances cell migration in SEC62 overexpressing cells resulting in a high rate of lymphatic metastasis and poorer overall prognosis in tumor tissue with a high Sec62 expression. We sought to further elucidate the function of Sec62 in breast cancer with special focus on its predictive role on the response to neoadjuvant chemotherapy. Materials and Methods All patients treated for primary breast cancer with neoadjuvant chemotherapy at the Department of Gynaecology and Obstetrics, Saarland University Hospital, Homburg, Germany between 01/2007 and 12/2018 were enrolled in this study. The study was approved by the Saarland institutional review board. Sec62 protein levels were analyzed in tumor tissue samples using immunohistochemistry (IHC). Sec62 immunoreactivity was evaluated by three independent examiners using the immunoreactive score (IRS) according to Remmele and Stegner (0-12). For the assessment of Sec62 protein expression in tumor cells, we rated Sec62 “negative” 0-3, “low” for a score of 4-8 and “high” for 9-12 as described in previous publications. IHC was performed on initial breast core biopsy (CB) tissue (pre-treatment) and on definite pathology specimen (PS) obtained during breast surgery after completion of neoadjuvant chemotherapy. Sec62 expression in both samples were compared and correlated with response to neoadjuvant chemotherapy evaluated pathologically using the semi-quantitative response to neoadjuvant chemotherapy scoring system by Sinn et al. ranging from 0 (no effect) to 4 (no tumor detectable). Additionally, Sec62 expression in tumor tissue was compared with the histologically tumor-free tissue of the same patient. Sec62 expression levels and correlation with response to neoadjuvant chemotherapy were compared using Wilcoxon signed-rank, Mann-Whitney and Pearson`s chi square test. Results 203 patients were assessed for eligibility. Nine cases were excluded, due to incomplete clinical information or insufficient slide quality, leaving 194 patients for final analysis. Median patient age was 54 (22-86) years and median response to neoadjuvant chemotherapy score of 2 (0-4). 20 patients (10 %) had luminal A, 46 (24 %) luminal B, 60 (31 %) Her2/neu positive and 68 (35 %) triple negative breast cancer. All analyzed slides showed an over-expression of Sec62 in breast cancer cells but no positive staining of physiologic breast tissue cells. Median Sec62 expression in core biopsies (CB) (8 (2-12)) was significantly higher compared to expression in final specimen (PS) (4 (0-12); p ≤ 0.01). Median difference between Sec62 expression of CB and PS was 2 (0-4). Regarding response to neoadjuvant chemotherapy patients with a low Sec62 expression in PS and a difference ≥ 6 between CB and PS showed a significant higher median response score compared to other patients (2 (0-4) vs. 1 (0-2); p ≤ 0.01; 4 (1-4) vs. 1 (0-4); p ≤ 0.01). When looking at breast cancer subtypes these effects were strongest in Her2/positive and triple negative patients and median Sec62 expression showed the highest decrease between CB and PS in these two subgroups (6 (-3-12); 2 (-6-12)). Conclusion We identified Sec62 as a potential biomarker for prediction of response to neoadjuvant chemotherapy in patients with primary breast cancer. This effect was observed to be strongest in patients with Her2/positive and triple negative breast cancer. Citation Format: Julia Caroline Radosa, Mariz Kasoha, Merle Doerk, Barbara Linxweiler, Maximilian Linxweiler, Florian Bochen, Rainer M Bohle, Matthias Wagner, Marc P Radosa, Erich-Franz Solomayer, Zoltan Ferenc Takacs. Role of Sec62 in prediction of response to neoadjuvant chemotherapy in patients with primary breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-10-28.

Identification of 3q oncogene SEC62 as a marker for distant metastasis and poor clinical outcome in invasive ductal breast cancer.

In previous studies, we have shown that SEC62 has an essential function in cell migration, epithelial-to-mesenchymal transition, and endoplasmic reticulum stress tolerance of cancer cells. SEC62 expression correlated with distant and lymph node metastasis and poor outcome in different cancer entities. In this initial study, we investigated SEC62 expression and its possible role as a prognostic and predictive biomarker in breast cancer (BC). Formalin-fixed, paraffin-embedded tissue samples of 53 BC patients were analyzed by immunohistochemistry. The immunoreactive score (IRS) according to Remmele and Stegner was evaluated and correlated with clinico-pathological findings and overall survival (OS). We found increased SEC62 protein levels in tumor tissue compared to tumor-free tissue samples from the same patients. Tumors with high SEC62 expression (IRS>8), or containing isolated cells with high SEC62 staining intensity, independent of the IRS, had more frequently distant metastases (48.4% vs. 18.2%; p = 0.024 and 47.4 vs. 6.7%; p = 0.005, respectively). Overall survival was significantly worse in BC patients with high SEC62 expression (SEC62 IRS>8) (54.8% vs. 81.8%; p = 0.011) and in cases with isolated high-intensity SEC62 staining cells independently of SEC62 IRS (55.3% vs 93.3%; p = 0.024). We are the first to describe the SEC62 expression and its correlation to clinicopathological parameters in mammary carcinoma. Our results suggest that SEC62 expression may serve as a prognostic marker for patients with invasive ductal breast cancer.

Components and Mechanisms of Import, Modification, Folding, and Assembly of Immunoglobulins in the Endoplasmic Reticulum

In mammalian cells, the endoplasmic reticulum (ER) plays a central role in biogenesis of secretory- and plasma membrane proteins as well as in cellular calcium (Ca(2+)) homeostasis. The protein biogenesis function involves an aqueous polypeptide conducting channel in the ER membrane, which is formed by the heterotrimeric Sec61 complex; the store- and receptor-controlled Ca(2+)- release function requires a steep ER to cytosol gradient, with more than 500μM free Ca(2+) in the ER and 50nM Ca(2+) in the cytosol. Recent work demonstrated that the Sec61 complex can transiently allow passive ER Ca(2+) efflux. Therefore, gating of the Sec61 channel has to be tightly regulated by substrates as well as allosteric effectors. The ER lumenal Hsp70-type molecular chaperone, immunoglobulin heavy-chain binding protein (BiP), together with its membrane resident co-chaperone Sec63 facilitates channel opening in a precursor specific manner. In addition, BiP, together with its lumenal co-chaperones, ERj3 and ERj6, as well as cytosolic Ca(2+)-calmodulin (CaM) in collaboration with the membrane resident Sec62 protein represent allosteric effectors for channel closure. In the course of the last couple of years several human diseases were linked to the Sec61 complex and its effectors and were termed Sec61-channelopathies.

Initial evidence for Sec62 as a prognostic marker in advanced head and neck squamous cell carcinoma.

Head and neck squamous cell carcinoma (HNSCC) is a malignancy with an increasing incidence. To aid with the selection of the most appropriate therapy, biomarkers have become a specific research focus. Sec62 is involved in endoplasmic reticulum stress tolerance and cell migration, and has been identified as a novel prognostic marker for non-small cell lung cancer. In addition, Sec62 may be a promising candidate in HNSCC. Pretreatment biopsies of 35 patients with locally advanced HNSCC, who were treated with definitive chemoradiation therapy without prior surgery, were examined for the expression of Sec62 protein, as well as the expression of epidermal growth factor receptor (EGFR), p16 and survivin proteins. Immunohistological results were correlated with patient overall survival (OS) and progression-free survival (PFS) times. In the present patient cohort, 12/35 cases (34%) demonstrated strong and 8/35 cases (23%) moderate Sec62 staining intensity. Additionally, in 11/35 cases (31%), weak staining was observed, and only 4/35 cases (11%) were Sec62-negative. Notably, a high Sec62 protein level was associated with a significantly poorer OS and PFS (P=0.020 and P=0.028, respectively). Furthermore, higher nuclear survivin expression showed a weak trend for poorer OS rate (P=0.079), whilst neither cytoplasmic survivin, EGFR nor p16 influenced OS or PFS significantly. The present study indicated that Sec62 is a promising prognostic marker for HNSCC. Increased Sec62 protein expression may indicate a poorer prognosis in advanced HNSCC. As the present study was focused on patients treated by chemoradiation therapy, further studies with larger patient cohorts and alternative treatment approaches are required in order to define the prognostic value of Sec62 in HNSCC.

Targeting cell migration and the endoplasmic reticulum stress response with calmodulin antagonists: a clinically tested small molecule phenocopy of SEC62 gene silencing in human tumor cells

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.

Sec62 Protein Mediates Membrane Insertion and Orientation of Moderately Hydrophobic Signal Anchor Proteins in the Endoplasmic Reticulum (ER)

Nascent chains are known to be targeted to the endoplasmic reticulum membrane either by a signal recognition particle (SRP)-dependent co-translational or by an SRP-independent post-translational translocation route depending on signal sequences. Using a set of model and cellular proteins carrying an N-terminal signal anchor sequence of controlled hydrophobicity and yeast mutant strains defective in SRP or Sec62 function, the hydrophobicity-dependent targeting efficiency and targeting pathway preference were systematically evaluated. Our results suggest that an SRP-dependent co-translational and an SRP-independent post-translational translocation are not mutually exclusive for signal anchor proteins and that moderately hydrophobic ones require both SRP and Sec62 for proper targeting and translocation to the endoplasmic reticulum. Further, defect in Sec62 selectively reduced signal sequences inserted in an N(in)-C(out) (type II) membrane topology, implying an undiscovered role of Sec62 in regulating the orientation of the signal sequence in an early stage of translocation.

Sec62 Bridges the Gap from 3q Amplification to Molecular Cell Biology in Non–Small Cell Lung Cancer

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.

Sec62 protein level is crucial for the ER stress tolerance of prostate cancer

We previously reported that over-expression of the SEC62 gene is a widespread phenomenon in prostate cancer. Since the use of endoplasmic reticulum (ER) stress-inducing substances such as thapsigargin in prostate cancer therapy is widely discussed in the literature, we investigated the influence of Sec62 protein content on the cellular response to these drugs. Growth effects were analyzed by real-time cell analysis and viability tests in DU145-cells representing an increased SEC62 expression or PC3- and LNCaP-cells representing a similar SEC62 expression compared to non-tumor cells. Ca(2+) -imaging in an established HeLa-system with fluorescent dye was used to study molecular effects of Sec62 depletion. We found a lower propensity toward apoptotic cell death after thapsigargin treatment for DU145 cells compared to PC3 or LNCaP and siRNA-mediated silencing of SEC62 resulted in a reduced viability of thapsigargin-treated PC3 cells, indicating that Sec62 functions in cellular stress response. Measurement of cytosolic [Ca(2+) ] demonstrated the influence of Sec62 on the cellular response to thapsigargin on a molecular level. Using real-time cell analysis, we observed the loss of androgen stimulation of LNCaP cells in the presence of thapsigargin, and an additional negative effect on cell growth of Sec62 depletion. Also, for PC3- and DU145-cells Sec62 depletion inhibited growth after thapsigargin treatment. Our data indicate a crucial function of Sec62 in the response to thapsigargin-induced ER stress. This will be of great significance on the background of elevated Sec62 protein levels in prostate cancer cells when treatment with thapsigargin analogs is considered.

Silencing of the SEC62 gene inhibits migratory and invasive potential of various tumor cells

Sec62 is part of the protein translocation apparatus in the membrane of the endoplasmic reticulum (ER). In yeast, Sec62 participates in the post-translational translocation of proteins into the ER, but its function in mammals remains elusive. Previously we described the amplification and over-expression of the SEC62 gene in prostate cancer cell lines and the protein has been described as a potential target gene in prostate cancer. In the current study we show that in the tumor tissue of prostate cancer patients Sec62 protein levels are elevated compared with tumor-free tissue derived from the same patients or from prostates of control group patients and that the higher Sec62 protein content correlates with an increasing de-differentiation of the cells. Therefore, up-regulation of Sec62 protein content indeed is a phenomenon associated with prostate cancer progression. Analysis of a multi-tissue tumor array showed that in addition to prostate cancer, overproduction of Sec62 is observed in various other tumors, most significantly in tumors of the lung and the thyroid. To examine the tumor-related functions of Sec62, we silenced the SEC62 gene in the prostate cancer cell-line PC3 as well as in a set of other tumor cell-lines with two different siRNAs. In general, after silencing of SEC62 the cell migration and the invasive potential of the cells was blocked or at least dramatically reduced while cell viability was hardly affected. Thus, the SEC62 gene may indeed be considered as a target gene in the therapy of various tumors.

Assembly of yeast Sec proteins involved in translocation into the endoplasmic reticulum into a membrane-bound multisubunit complex

Secretory-protein translocation into the endoplasmic reticulum (ER) is thought to be catalysed by integral membrane proteins. Genetic selections uncovered three Saccharomyces cerevisiae genes (SEC61, SEC62 and SEC63), mutations in which block import of precursor proteins into the ER lumen in vivo and in vitro. The DNA sequences of SEC62 and SEC63 predict multispanning membrane proteins, and biochemical characterization of the SEC62 protein (Sec62) confirms that it is an integral ER membrane protein. Here we show that Sec61, Sec62 and Sec63 are assembled with two additional proteins into a multisubunit membrane-associated complex. These results confirm previous predictions, based upon genetic interactions between the SEC genes, that Sec61, Sec62 and Sec63 act together to facilitate protein translocation into the ER.