Deleted in liver cancer 2 suppresses cell growth via the regulation of the Raf-1-ERK1/2-p70S6K signalling pathway

Loss of STARD13 contributes to aggressive phenotype transformation and poor prognosis in papillary thyroid carcinoma

PURPOSE

StAR Related Lipid Transfer Domain Containing 13 (STARD13) serves as a tumor suppressor and has been characterized in several types of malignancies. However, the role and the molecular mechanism of STARD13 in regulating the progression of papillary thyroid carcinoma (PTC) remain underexplored.

METHODS

The gene expression and clinical information of thyroid cancer were downloaded using "TCGAbiolinks" R package. Quantitative PCR and immunohistochemical staining were conducted to detect the expression of STARD13 in clinical tumor and adjacent non-tumor samples. Wound-healing assay, Transwell assay and 3D spheroid invasion assay were performed to evaluate the migratory and invasive capacities of PTC cells. Cell proliferation ability was determined by CCK-8 assay, colony formation assay and 5-ethynyl-2'-deoxyuridine (EdU) incorporation assay. The alterations of indicated proteins were detected by Western blotting.

RESULTS

In the present study, we found that STARD13 was significantly underexpressed in PTC, which was correlated with poor prognosis. Downregulation of STARD13 might be due to methylation of promoter region. Loss-and gain-of-function experiments demonstrated that STARD13 impeded migratory and invasive capacities of PTC cells in vitro and in vivo. In addition, we found that STARD13 regulated the morphology of PTC cells and inhibited epithelial-mesenchymal transition (EMT).

CONCLUSION

Our results suggest that STARD13 acts as a metastasis suppressor and might be a potential therapeutic target in PTC.

Ras superfamily GTPase activating proteins in cancer: Potential therapeutic targets?

To search more therapeutic strategies for Ras-mutant tumors, regulators of the Ras superfamily involved in the GTP/GDP (guanosine triphosphate/guanosine diphosphate) cycle have been well concerned for their anti-tumor potentials. GTPase activating proteins (GAPs) provide the catalytic group necessary for the hydrolysis of GTPs, which accelerate the switch by cycling between GTP-bound active and GDP-bound inactive forms. Inactivated GAPs lose their function in activating GTPase, leading to the continuous activation of downstream signaling pathways, uncontrolled cell proliferation, and eventually carcinogenesis. A growing number of evidence has shown the close link between GAPs and human tumors, and as a result, GAPs are believed as potential anti-tumor targets. The present review mainly summarizes the critically important role of GAPs in human tumors by introducing the classification, function and regulatory mechanism. Moreover, we comprehensively describe the relationship between dysregulated GAPs and the certain type of tumor. Finally, the current status, research progress, and clinical value of GAPs as therapeutic targets are also discussed, as well as the challenges and future direction in the cancer therapy.

miR-182-5p Serves as an Oncogene in Lung Adenocarcinoma through Binding to STARD13

Lung cancer as one of the commonest invasive malignancies is featured by high morbidity and mortality, wherein lung adenocarcinoma (LUAD) is the most prevalent subtype. Accumulating evidence exhibited that microRNAs are involved in LUAD occurrence and progression. In this study, miR-182-5p was observed to increase in both LUAD tissue and cell lines. Overexpression of miR-182-5p could prominently facilitate cell proliferation, migration, and invasion in LUAD. Through bioinformatics analysis, STARD13 was theorized as the target gene of miR-182-5p, which was lowly expressed in LUAD. Further molecular experiments manifested that miR-182-5p bound to the 3'-untranslated region of STARD13, and there was an inverse correlation between STARD13 and miR-182-5p in LUAD. Rescue experiments demonstrated that silencing STARD13 conspicuously restored the inhibitory effect of decreased miR-182-5p on cell proliferation, migration, and invasion in LUAD. Together, our findings revealed novel roles of the miR-182-5p/STARD13 axis in LUAD progression.

StarD13 differentially regulates migration and invasion in prostate cancer cells

Prostate cancer is the second most commonly diagnosed cancer in men and one of the main leading causes of cancer deaths among men worldwide. Rapid uncontrolled growth and the ability to metastasize to other sites are key hallmarks in cancer development and progression. The Rho family of GTPases and its activators the GTPase-activating proteins (GAPs) are required for regulating cancer cell proliferation and migration. StarD13 is a GAP for Rho GTPases, specifically for RhoA and Cdc42. We have previously shown that StarD13 acts as a tumor suppressor in astrocytoma as well as breast and colorectal cancer. In this study, we performed a functional comparative analysis of StarD13 targets/and or interacting molecules to understand the general role that StarD13 plays in cancers. Our data highlight the importance of StarD13 in modulating several hallmarks of cancer. Findings from database mining and immunohistochemistry revealed that StarD13 is underexpressed in prostate cancers, in addition knocking down Stard13 increased cancer cell proliferation, consistent with its role as a tumor suppressor. Stard13 depletion, however, led to an increase in cell adhesion, which inhibited 2D cell migration. Most interestingly, StarD13 depletion increases invasion and matrix degradation, at least in part, through its regulation of Cdc42. Altogether, the data presented suggest that StarD13 acts as a tumor suppressor inhibiting prostate cancer cell invasion.

Simultaneous Combination of the CDK4/6 Inhibitor Palbociclib With Regorafenib Induces Enhanced Anti-tumor Effects in Hepatocarcinoma Cell Lines

Advanced hepatocarcinoma (HCC) is an aggressive malignancy with poor prognosis and limited treatment options. Alterations of the cyclin D-CDK4/6-Rb pathway occur frequently in HCC, providing the rationale for its targeting at least in a molecular subset of HCC. In a panel of HCC cell lines, we investigated whether the CDK4/6 inhibitor palbociclib might improve the efficacy of regorafenib, a powerful multi-kinase inhibitor approved as second-line treatment for advanced HCC after sorafenib failure and currently under clinical investigation as first-line therapy in combination with immunotherapy. In Rb-proficient cells, the simultaneous drug combination, but not the sequential schedules, inhibited cell proliferation, either in short or in long-term experiments, and induced cell death more strongly than individual treatments. Moreover, the combination significantly reduced spheroid cell growth and inhibited cell migration/invasion. The superior efficacy of palbociclib plus regorafenib emerged also under hypoxia and was associated with a significant down-regulation of CDK4/6-Rb-myc and mTORC1/p70S6K signaling. Moreover, regorafenib suppressed palbociclib-induced expression of cyclin D1 contributing to the cytotoxic effects of the combination. Besides these inhibitory effects on cell viability/proliferation, palbociclib and regorafenib reduced glucose uptake, although this effect was dependent on the cell model and on the oxygen availability (normoxia or hypoxia). Palbociclib and regorafenib combination impaired glucose uptake and utilization, down-regulating basal and hypoxia-induced expression of HIF-1α, HIF-2α, GLUT-1, and MCT4 proteins as well as the activity/expression of glycolytic enzymes (HK2, PFKP, aldolase A, PKM2). In addition, regorafenib alone reduced mitochondrial respiration. The combined treatment impaired glucose metabolism and respiration without enhancing the effects of the single agents. Our findings provide pre-clinical evidence for the effectiveness of palbociclib and regorafenib combination in HCC cell models.

StarD13: a potential star target for tumor therapeutics

StarD13 is a tumor suppressor and a GTPase activating protein (GAP) for Rho GTPases. Thus, StarD13 regulates cell survival pathways and induces apoptosis in a p53-dependent and independent manners. In tumors, StarD13 is either downregulated or completely inhibited, depending on the tumor type. As such, and through the dysregulation of Rho GTPases, this affects adhesion dynamics, actin dynamics, and leads to an increase or a decrease in tumor metastasis depending on the tumor grade and type. Being a key regulatory protein, StarD13 is a potential promising candidate for therapeutic approaches. This paper reviews the key characteristics of this protein and its role in tumor malignancies.

Non-canonical Raf-1/p70S6K signalling in non-small-cell lung cancer

Lung cancer is the leading cause of cancer-related death globally, with non-small-cell lung cancer (NSCLC) being the predominant subtype. Overall survival remains low for NSCLC patients, and novel targets are needed to improve outcome. Raf-1 is a key component of the Ras/Raf/MEK signalling pathway, but its role and downstream targets in NSCLC are not completely understood. Our previous study indicated a possible correlation between Raf-1 levels and ribosomal protein S6 kinase (p70S6K) function. In this study, we aimed to investigate whether p70S6K is a downstream target of Raf-1 in NSCLC. Raf-1 was silenced in NSCLC cell lines by using small hairpin RNA, and Raf-1 and p70S6K protein levels were measured via Western blot. p70S6K was then overexpressed following Raf-1 knock-down; then, cell proliferation, apoptosis and the cell cycle in NSCLC cell lines were examined. Tumour xenografts with NSCLC cells were then transplanted for in vivo study. Tumours were measured and weighed, and Raf-1 and p70S6K expression, cell proliferation and apoptosis were examined in tumour tissues by Western blot, Ki-67 staining and TUNEL staining, respectively. When Raf-1 was silenced, p70S6K protein levels were markedly decreased in the A549 and H1299 NSCLC cell lines. A significant decrease in NSCLC cell proliferation, a profound increase in apoptosis and cell cycle arrest were observed in vitro following Raf-1 knock-down. Overexpression of p70S6K after Raf-1 depletion effectively reversed these effects. Xenograft studies confirmed these results in vivo. In conclusion, Raf-1 targets p70S6K as its downstream effector to regulate NSCLC tumorigenicity, making Raf-1/p70S6K signalling a promising target for NSCLC treatment.

Effect of Selective Serotonin (5-HT)2B Receptor Agonist BW723C86 on Epidermal Growth Factor/Transforming Growth Factor-α Receptor Tyrosine Kinase and Ribosomal p70 S6 Kinase Activities in Primary Cultures of Adult Rat Hepatocytes

Serotonin (5-hydroxytryptamine; 5-HT) can induce hepatocyte DNA synthesis and proliferation by autocrine secretion of transforming growth factor (TGF)-α through 5-HT_2B receptor/phospholipase C (PLC)/Ca²⁺ and a signaling pathway involving epidermal growth factor (EGF)/TGF-α receptor tyrosine kinase (RTK)/extracellular signal-regulated kinase 2 (ERK2)/mammalian target of rapamycin (mTOR). In the present study, we investigated whether 5-HT or a selective 5-HT_2B receptor agonist BW723C86, would stimulate phosphorylation of TGF-α RTK and ribosomal p70 S6 kinase (p70S6K) in primary cultures of adult rat hepatocytes. Western blotting analysis was used to detect 5-HT- or BW723C86 (10^-6 M)-induced phosphorylation of EGF/TGF-α RTK and p70S6K. Our results showed that 5-HT- or BW723C86 (10^-6 M)-induced phosphorylation of EGF/TGF-α RTK peaked at between 5 and 10 min. On the other hand, 5-HT- or BW723C86 (10^-6 M)-induced phosphorylation of p70S6K peaked at about 30 min. Furthermore, a selective 5-HT_2B receptor antagonist LY272015, a specific PLC inhibitor U-73122, a membrane-permeable Ca²⁺ chelator BAPTA/AM, an L-type Ca²⁺ channel blocker verapamil, somatostatin, and a specific p70S6K inhibitor LY2584702 completely abolished the phosphorylation of p70S6K induced by both 5-HT and BW723C86. These results indicate that phosphorylation of p70S6K is dependent on the 5-HT_2B-receptor-mediated autocrine secretion of TGF-α. In addition, these results demonstrate that the hepatocyte proliferating action of 5-HT and BW723C86 are mediated by phosphorylation of p70S6K, a downstream element of the EGF/TGF-α RTK signaling pathway.

DLC2 operates as a tumor suppressor gene in breast cancer via the RhoGTPase pathway

Deleted in liver cancer 2 (DLC2) is a tumor suppressor, associated with various types of cancer. The aim of the present study was to analyze the expression of DLC2 in breast cancer, its clinical significance and its effect on breast cancer cell behavior. The expression of DLC2 was evaluated by immunohistochemistry in 131 cases of breast cancer. Associations among DLC2 expression and clinicopathological features were analyzed, and its effects on proliferation, motility, migration and invasion in DLC2-knockdown breast cancer cell lines were observed. The results indicated that DLC2 was expressed in 42.75% of breast cancer cases (56/131) and in 79.39% of adjacent normal tissues (104/131). Lower expression of DLC2 in breast cancer was associated with tumor differentiation (P<0.001), lymph node metastasis (P<0.001) and poor prognosis (P<0.001). The silencing of the DLC2 gene in human breast cancer cell indicated an increased number of cells entering S phase, and increased abilities of clone formation, cell migration and invasion. Downregulated expression of DLC2 was associated with activated Ras homolog family member A and decreased Rac family small GTPase 1, cell division cycle 42 and Rho-associated protein kinase-2 expression levels, indicating that DLC2 may serve a regulatory function in breast cancer cell proliferation and invasion via the RhoGTPase pathway. The results of the present study suggested that DLC2 serves as a suppressor gene in the development of breast cancer and may be a prognostic marker for patients with breast cancer.

Downregulation of STARD8 in gastric cancer and its involvement in gastric cancer progression

Objective

Rho-GTPases play a pivotal role in a wide variety of signal transduction pathways and are associated with a great number of human carcinomas. STARD8, which is a Rho-GTPase-activating protein, has been proposed as a tumor suppressor gene, but its role in gastric cancer remains elusive. In this study, we investigate the expression of STARD8 in gastric cancer and its association with gastric cancer progression.

Materials and methods

One normal gastric mucosa cell line for example GES1 and six human gastric cancer cell lines such as AGS, MGC803, MKN45, SGC7901, HGC27 and BGC823 were utilized to analyze STARD8 mRNA and protein levels by reverse transcription polymerase chain reaction (RT-PCR) and Western blot. A total of 70 paired gastric tissues including corresponding nonmalignant gastric tissues and cancer tissues were utilized to analyze the protein expression of STARD8 using immunohistochemistry, and the correlation between STARD8 level and clinicopathological features was also evaluated.

Results

STARD8 was found to be downregulated in primary gastric cancer cells and tissues compared with the normal gastric mucosa cell line, GES1, and corresponding nonmalignant gastric tissues, while its decreased expression was significantly associated with TNM stage, lymph node metastasis and differentiation (p<0.05).

Conclusion

There is significantly decreased expression of STARD8 in gastric cancer cells and tissues, and its expression may contribute to gastric tumorigenesis.

Displacement of Bax by BMF Mediates STARD13 3'UTR-Induced Breast Cancer Cells Apoptosis in an miRNA-Depedent Manner

The balance of pro- and antiapoptotic gene expression programs dominates the apoptotic progress of cancer cells. We previously demonstrated that STARD13 3'UTR suppressed breast cancer metastasis via inhibiting epithelial-mesenchymal transition (EMT). However, the roles of STARD13 3'UTR in breast cancer apoptosis remain elusive. Here, we identified that STARD13 3'UTR promoted cell apoptosis in vitro and in vivo. Mechanistically, STARD13 3'UTR acted as a ceRNA for BMF (Bcl-2 modifying factor), thus increasing BMF expression in an miRNA-dependent manner. Meanwhile, STARD13 3'UTR enhanced the interaction of BMF/Bcl-2 to release Bax (Bcl-2 associated X protein) in breast cancer cells. Finally, we verified the ceRNA relationship between STARD13 and BMF in vivo. Collectively, these findings suggest that STARD13 3'UTR could act as a ceRNA for BMF to promote apoptosis and recognize STARD13 3'UTR as a potential therapeutic target in breast cancer cells.

Ribosomal proteins: insight into molecular roles and functions in hepatocellular carcinoma

Ribosomes, which are important sites for the synthesis of proteins related to expression and transmission of genetic information in humans, have a complex structure and diverse functions. They consist of a variety of ribosomal proteins (RPs), ribosomal RNAs (rRNAs) and small nucleolar RNAs. Owing to the involvement of ribosomes in many important biological processes of cells, their major components, rRNAs and RPs, have an important role in human diseases, including the initiation and evolvement of malignancies. However, the main mechanisms underlying the involvement of ribosomes in cancer remain unclear. This review describes the crucial role of ribosomes in various common malignant tumors; in particular, it examines the effects of RPs, including S6, the receptor for activated C-kinase and RPS15A, on the development and progression of hepatocellular carcinoma.

Human mesenchymal stromal cells modulate T-cell immune response via transcriptomic regulation

BACKGROUND AIMS

Mesenchymal stromal cells (MSCs) have been identified as pan-immunosuppressant in various in vitro and in vivo inflammatory models. Although the immunosuppressive activity of MSCs has been explored in various contexts, the precise molecular signaling pathways that govern inhibitory functions remain poorly elucidated.

METHODS

By using a microarray-based global gene expression profiling system, this study aimed to decipher the underlying molecular pathways that may mediate the immunosuppressive activity of umbilical cord-derived MSCs (UC-MSCs) on activated T cells.

RESULTS

In the presence of UC-MSCs, the proliferation of activated T cells was suppressed in a dose-depended manner by cell-to-cell contact mode via an active cell-cycle arrest at the G0/G1 phase of the cell cycle. The microarray analysis revealed that particularly, IFNG, CXCL9, IL2, IL2RA and CCND3 genes were down-regulated, whereas IL11, VSIG4, GFA1, TIMP3 and BBC3 genes were up-regulated by UC-MSCs. The dysregulated gene clusters associated with immune-response-related ontologies, namely, lymphocyte proliferation or activation, apoptosis and cell cycle, were further analyzed.

CONCLUSIONS

Among the nine canonical pathways identified, three pathways (namely T-helper cell differentiation, cyclins and cell cycle regulation, and gap/tight junction signalling pathways) were highly enriched with these dysregulated genes. The pathways represent putative molecular pathways through which UC-MSCs elicit immunosuppressive activity toward activated T cells. This study provides a global snapshot of gene networks and pathways that contribute to the ability of UC-MSCs to suppress activated T cells.

The tumour suppressor DLC2 ensures mitotic fidelity by coordinating spindle positioning and cell-cell adhesion

Dividing epithelial cells need to coordinate spindle positioning with shape changes to maintain cell–cell adhesion. Microtubule interactions with the cell cortex regulate mitotic spindle positioning within the plane of division. How the spindle crosstalks with the actin cytoskeleton to ensure faithful mitosis and spindle positioning is unclear. Here we demonstrate that the tumour suppressor DLC2, a negative regulator of Cdc42, and the interacting kinesin Kif1B coordinate cell junction maintenance and planar spindle positioning by regulating microtubule growth and crosstalk with the actin cytoskeleton. Loss of DLC2 induces the mislocalization of Kif1B, increased Cdc42 activity and cortical recruitment of the Cdc42 effector mDia3, a microtubule stabilizer and promoter of actin dynamics. Accordingly, DLC2 or Kif1B depletion promotes microtubule stabilization, defective spindle positioning, chromosome misalignment and aneuploidy. The tumour suppressor DLC2 and Kif1B are thus central components of a signalling network that guides spindle positioning, cell–cell adhesion and mitotic fidelity.

Epithelial cells must position their mitotic spindle correctly to maintain cell–cell adhesion. Here Vitiello et al. show that the tumour suppressor DLC2 and the mitotic kinesin Kif1b coordinate microtubule–actin interactions upstream of mDia3, guiding spindle positioning and mitotic fidelity.

The STAR of the DLC family

RhoGTPases are defined as a family of 20 small G proteins playing important roles in almost every cellular process. RhoGTPases are guanine nucleotide-binding proteins existing in two forms: the active form which is GTP bound and the inactive one that being GDP bound. RhoGTPase-activating proteins known as RhoGAPs constitute one of the major classes of regulators of RhoGTPases. They act as negative regulators of the RhoGTPases by enhancing their slow intrinsic GTPase activity. STARD13, a GTPase activating protein (GAP) for RhoGTPases, has been described as a tumor suppressor in hepatocellular carcinoma. In the present review, we discuss the family of RhoGTPases, their regulation and their RhoGAPs, focusing mainly on STARD13.

Expression of deleted in liver cancer 2 in colorectal cancer and its correlation with clinicopathological parameters

Deleted in liver cancer 2 (DLC2) has been identified as a tumor suppressor gene. DLC2 is closely related to deleted in liver cancer 1 (DLC1) and is located at chromosome 13q12.3. The expression of DLC2 mRNA has been found in a wide range of cancers, including colorectal cancer (CRC). However, there are no available data on the expression status of DLC2 in Chinese patients with CRC and its correlation with clinicopathological parameters. The aim of this study was to investigate the expression levels of DLC2 mRNA and protein in Chinese patients with CRC and the correlation between DLC2 expression and clinicopathological parameters. To this end, real-time PCR, western blotting and immunohistochemistry were employed to detect DLC2 mRNA and protein expression in CRC and pericarcinomatous intestinal tissue (PCIT) specimens, which were obtained from 102 Chinese CRC patients who underwent surgical resection between October 2010 and February 2012. We also analyzed the correlations between DLC2 expression and the clinicopathological parameters of CRC patients. Our results showed that CRC tissues had significantly lower levels of DLC2 mRNA compared with PCITs (P<0.05); however, the protein expression levels were not significantly different between CRCs and PCITs. The expression levels of DLC2 mRNA and protein were significantly correlated with lymph node metastasis and tumor TNM stage. Additionally, DLC2 mRNA expression levels were also correlated with tumor histopathological degree (P<0.05). Collectively, our results suggest that the downregulated expression of DLC2 participates in CRC carcinogenesis, invasion and lymph node metastasis. Furthermore, our results imply that DLC2 is be a potential prognostic marker for CRC patients.

MicroRNA-125b induces metastasis by targeting STARD13 in MCF-7 and MDA-MB-231 breast cancer cells

MicroRNAs (miRNAs) are a class of small noncoding RNAs that regulate gene expression by targeting mRNAs to trigger either translation repression or mRNA degradation. miR-125b is down-regulated in human breast cancer cells compared with the normal ones except highly metastatic tumor cells MDA-MB-231. However, few functional studies were designed to investigate metastatic potential of miR-125b. In this study, the effects of miR-125b on metastasis in human breast cancer cells were studied, and the targets of miR-125b were also explored. Transwell migration assay, cell wound healing assay, adhesion assay and nude mice model of metastasis were utilized to investigate the effects of miR-125b on metastasis potential in vitro and in vivo. In addition, it was implied STARD13 (DLC2) was a direct target of miR-125b by Target-Scan analysis, luciferase reporter assay and western blot. Furthermore, activation of STARD13 was identified responsible for metastasis induced by miR-125b through a siRNA targeting STARD13. qRT-PCR, immunofluorescent assay and western blot was used to observe the variation of Vimentin and α-SMA in breast cancer cells. In summary, our study provided new insights into the function of miR-125b during the metastasis of breat cancer cells and also suggested the role of miR-125b in pro-metastasis by targeting STARD13.

Deleted in liver cancer protein family in human malignancies (Review)

The Deleted in Liver Cancer (DLC) protein family comprises proteins that exert their function mainly by the Rho GTPase-activating protein (GAP) domain and by regulation of the small GTPases. Since Rho GTPases are key factors in cell proliferation, polarity, cytoskeletal remodeling and migration, the aberrant function of their regulators may lead to cell transformation. One subgroup of these proteins is the DLC family. It was found that the first identified gene from this family, DLC1, is often lost in hepatocellular carcinoma and may be involved as a tumor suppressor in the liver. Subsequent studies evaluated the hypothesis that the DLC1 gene acts as a tumor suppressor, not only in liver cancer, but also in other types of cancer. Following DLC1, two other members of the DLC protein family, DLC2 and DLC3, were identified. However, limited published data are available concerning the role of these proteins in malignant transformation. This review focuses on the structure and the role of DLC1 and its relatives in physiological conditions and summarizes data published thus far regarding DLC function in the neoplastic process.