A novel tumor suppressor function of Kindlin-3 in solid cancer

Inactivation of kindlin-3 increases human melanoma aggressiveness through the collagen-activated tyrosine kinase receptor DDR1

The role of the focal adhesion protein kindlin-3 as a tumor suppressor and its interaction mechanisms with extracellular matrix constitute a major field of investigation to better decipher tumor progression. Besides the well-described role of kindlin-3 in integrin activation, evidence regarding modulatory functions between melanoma cells and tumor microenvironment are lacking and data are needed to understand mechanisms driven by kindlin-3 inactivation. Here, we show that kindlin-3 inactivation through knockdown or somatic mutations increases BRAFV600mut melanoma cells oncogenic properties via collagen-related signaling by decreasing cell adhesion and enhancing proliferation and migration in vitro, and by promoting tumor growth in mice. Mechanistic analysis reveals that kindlin-3 interacts with the collagen-activated tyrosine kinase receptor DDR1 (Discoidin domain receptor 1) modulating its expression and its interaction with β1-integrin. Kindlin-3 knockdown or mutational inactivation disrupt DDR1/β1-integrin complex in vitro and in vivo and its loss improves the anti-proliferative effect of DDR1 inhibition. In agreement, kindlin-3 downregulation is associated with DDR1 over-expression in situ and linked to worse melanoma prognosis. Our study reveals a unique mechanism of action of kindlin-3 in the regulation of tumorigenesis mediated by the collagen-activated tyrosine kinase receptor DDR1 thus paving the way for innovative therapeutic targeting approaches in melanoma.

Opposite roles of Kindlin orthologs in cell survival and proliferation

OBJECTIVE

It is unclear why adhesion-dependent cells such as epithelium undergo anoikis without anchorage, while adhesion-independent blood cells thrive in suspension. The adhesive machinery of these cells is similar, with the exception of Kindlin orthologs, Kindlin 2 (K2) and Kindlin 3 (K3). Here we address how Kindlins control cell survival and proliferation in anchorage-dependent and independent cells.

MATERIAL AND METHODS

To demonstrate the opposite roles of Kindlin's in cell survival we utilized in vivo and in vitro models and K3 and K2 knockdown and knockin cells. We used human lymphocytes from the K3 deficient patients in tumour model, K3 knockout and knockin macrophages and K2 knockout and knockin MEF cells for experiments in under conditions of adhesion and in suspension.

RESULTS

Depletion of K3 promotes cell proliferation and survival of anchorage-independent cells regardless of cell attachment. In contrast, the absence of K2 in anchorage-dependent cells accelerates apoptosis and limits proliferation. K3 deficiency promotes human lymphoma growth and survival in vivo. Kindlins' interaction with paxillin, is critical for their differential roles in cell anchorage. While disruption of K2-paxillin binding leads to increased apoptosis, the lack of K3-paxillin binding has an opposite effect in adhesion-independent cells.

CONCLUSION

Kindlin ortologs and their interaction to cytoskeletal protein paxillin define the mechanisms of anchorage dependence. Our study identifies the key elements of the cell adhesion machinery in cell survival and tumour metastasis, proposing possible targets for tumour treatment.

Blockage of PD-L1 by FERMT3-mediated Wnt/β-catenin signaling regulates chemoresistance and immune evasion of colorectal cancer cells

Colorectal cancer (CRC) constitutes a major public health problem due to the high rate of morbidity and mortality. Chemotherapy and immunotherapy are the major and promising strategies for cancer patients including CRC; nevertheless, chemoresistance and immune escape limit the final efficacy of above approaches. FERMT3 has been proved to exert the critical role in immune system and contradictive effects on cancer progression. In this study, bioinformatics database analysis and clinical specimen detection both corroborated the down-regulation of FERMT3 in CRC tissues and cells. Of interest, overexpression of FERMT3 suppressed CRC cell invasion and sensitized cells to 5-fluorouracil (5-FU) by reducing cell viability and increasing cell apoptosis and caspase-3 activity. Noticeably, FERMT3 up-regulation enhanced natural killer (NK) cells activation by increasing secretions of IFN-γ and TNF-α when NK cells were co-cultured with CRC cells. Importantly, up-regulation of FERMT3 promoted NK cell-mediated killing of CRC cells. Mechanically, FERMT3 inhibited the aberrant activation of Wnt/β-catenin signaling and the subsequent PD-L1 expression in CRC cells. Moreover, targeting PD-L1 suppressed CRC cell invasion, 5-FU resistance and NK cells-mediated tumor killing. Additionally, reactivating the Wnt/β-catenin signaling with a specific WNT agonist CAS 853220-52-7 overturned the efficacy of FERMT3 overexpression against CRC cell invasion, 5-FU chemoresistance and cell susceptibility to NK cell-mediated cytotoxicity. Thus, the current findings substantiate that FERMT3 elevation may attenuate CRC cell chemoresistance and NK cell-mediated immune response to tumor cells by inhibiting Wnt/β-catenin-PD-L1 signaling. Therefore, FERMT3 elevation may be a promising therapeutic approach to overcome chemoresistance and immune evasion in CRC. This article is protected by copyright. All rights reserved.

New insights into the molecular mechanisms of ROR1, ROR2, and PTK7 signaling from the proteomics and pharmacological modulation of ROR1 interactome

ROR1, ROR2, and PTK7 are Wnt ligand-binding members of the receptor tyrosine kinase family. Despite their lack of catalytic activity, these receptors regulate skeletal, cardiorespiratory, and neurological development during embryonic and fetal stages. However, their overexpression in adult tissue is strongly connected to tumor development and metastasis, suggesting a strong pharmacological potential for these molecules. Wnt5a ligand can activate these receptors, but lead to divergent signaling and functional outcomes through mechanisms that remain largely unknown. Here, we developed a cellular model by stably expressing ROR1, ROR2, and PTK7 in BaF3 cells that allowed us to readily investigate side-by-side their signaling capability and functional outcome. We applied proteomic profiling to BaF3 clones and identified distinctive roles for ROR1, ROR2, and PTK7 pseudokinases in modulating the expression of proteins involved in cytoskeleton dynamics, apoptotic, and metabolic signaling. Functionally, we show that ROR1 expression enhances cell survival and Wnt-mediated cell proliferation, while ROR2 and PTK7 expression is linked to cell migration. We also demonstrate that the distal C-terminal regions of ROR1 and ROR2 are required for receptors stability and downstream signaling. To probe the pharmacological modulation of ROR1 oncogenic signaling, we used affinity purification coupled to mass spectrometry (AP-MS) and proximity-dependent biotin identification (BioID) to map its interactome before and after binding of GZD824, a small molecule inhibitor previously shown to bind to the ROR1 pseudokinase domain. Our findings bring new insight into the molecular mechanisms of ROR1, ROR2, and PTK7, and highlight the therapeutic potential of targeting ROR1 with small molecule inhibitors binding to its vestigial ATP-binding site.

FERMT3 mediates cigarette smoke-induced epithelial-mesenchymal transition through Wnt/β-catenin signaling

Background

Cigarette smoking is a major risk factor for chronic obstructive pulmonary disease (COPD) and lung cancer. Epithelial–mesenchymal transition (EMT) is an essential pathophysiological process in COPD and plays an important role in airway remodeling, fibrosis, and malignant transformation of COPD. Previous studies have indicated FERMT3 is downregulated and plays a tumor-suppressive role in lung cancer. However, the role of FERMT3 in COPD, including EMT, has not yet been investigated.

Methods

The present study aimed to explore the potential role of FERMT3 in COPD and its underlying molecular mechanisms. Three GEO datasets were utilized to analyse FERMT3 gene expression profiles in COPD. We then established EMT animal models and cell models through cigarette smoke (CS) or cigarette smoke extract (CSE) exposure to detect the expression of FERMT3 and EMT markers. RT-PCR, western blot, immunohistochemical, cell migration, and cell cycle were employed to investigate the potential regulatory effect of FERMT3 in CSE-induced EMT.

Results

Based on Gene Expression Omnibus (GEO) data set analysis, FERMT3 expression in bronchoalveolar lavage fluid was lower in COPD smokers than in non-smokers or smokers. Moreover, FERMT3 expression was significantly down-regulated in lung tissues of COPD GOLD 4 patients compared with the control group. Cigarette smoke exposure reduced the FERMT3 expression and induces EMT both in vivo and in vitro. The results showed that overexpression of FERMT3 could inhibit EMT induced by CSE in A549 cells. Furthermore, the CSE-induced cell migration and cell cycle progression were reversed by FERMT3 overexpression. Mechanistically, our study showed that overexpression of FERMT3 inhibited CSE-induced EMT through the Wnt/β-catenin signaling.

Conclusions

In summary, these data suggest FERMT3 regulates cigarette smoke-induced epithelial–mesenchymal transition through Wnt/β-catenin signaling. These findings indicated that FERMT3 was correlated with the development of COPD and may serve as a potential target for both COPD and lung cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-021-01881-y.

High Throughput Transcriptome Data Analysis and Computational Verification Reveal Immunotherapy Biomarkers of Compound Kushen Injection for Treating Triple-Negative Breast Cancer

Background

Although notable therapeutic and prognostic benefits of compound kushen injection (CKI) have been found when it was used alone or in combination with chemotherapy or radiotherapy for triple-negative breast cancer (TNBC) treatment, the effects of CKI on TNBC microenvironment remain largely unclear. This study aims to construct and validate a predictive immunotherapy signature of CKI on TNBC.

Methods

The UPLC-Q-TOF-MS technology was firstly used to investigate major constituents of CKI. RNA sequencing data of CKI-perturbed TNBC cells were analyzed to detect differential expression genes (DEGs), and the GSVA algorithm was applied to explore significantly changed pathways regulated by CKI. Additionally, the ssGSEA algorithm was used to quantify immune cell abundance in TNBC patients, and these patients were classified into distinct immune infiltration subgroups by unsupervised clustering. Then, prognosis-related genes were screened from DEGs among these subgroups and were further overlapped with the DEGs regulated by CKI. Finally, a predictive immunotherapy signature of CKI on TNBC was constructed based on the LASSO regression algorithm to predict mortality risks of TNBC patients, and the signature was also validated in another TNBC cohort.

Results

Twenty-three chemical components in CKI were identified by UPLC-Q-TOF-MS analysis. A total of 3692 DEGs were detected in CKI-treated versus control groups, and CKI significantly activated biological processes associated with activation of T, natural killer and natural killer T cells. Three immune cell infiltration subgroups with 1593 DEGs were identified in TNBC patients. Then, two genes that can be down-regulated by CKI with hazard ratio (HR) > 1 and 26 genes that can be up-regulated by CKI with HR < 1 were selected as key immune- and prognosis-related genes regulated by CKI. Lastly, a five-gene prognostic signature comprising two risky genes (MARVELD2 and DYNC2I2) that can be down-regulated by CKI and three protective genes (RASSF2, FERMT3 and RASSF5) that can be up-regulated by CKI was developed, and it showed a good performance in both training and test sets.

Conclusions

This study proposes a predictive immunotherapy signature of CKI on TNBC, which would provide more evidence for survival prediction and treatment guidance in TNBC as well as a paradigm for exploring immunotherapy biomarkers in compound medicines.

Quantitative Proteomics Identifies Secreted Diagnostic Biomarkers as well as Tumor-Dependent Prognostic Targets for Clear Cell Renal Cell Carcinoma

Clear cell renal cell carcinoma (ccRCC) is the third most common and most malignant urological cancer, with a 5-year survival rate of 10% for patients with advanced tumors. Here, we identified 10,160 unique proteins by in-depth quantitative proteomics, of which 955 proteins were significantly regulated between tumor and normal adjacent tissues. We verified four putatively secreted biomarker candidates, namely, PLOD2, FERMT3, SPARC, and SIRPα, as highly expressed proteins that are not affected by intratumor and intertumor heterogeneity. Moreover, SPARC displayed a significant increase in urine samples of patients with ccRCC, making it a promising marker for the detection of the disease in body fluids. Furthermore, based on molecular expression profiles, we propose a biomarker panel for the robust classification of ccRCC tumors into two main clusters, which significantly differed in patient outcome with an almost three times higher risk of death for cluster 1 tumors compared with cluster 2 tumors. Moreover, among the most significant clustering proteins, 13 were targets of repurposed inhibitory FDA-approved drugs. Our rigorous proteomics approach identified promising diagnostic and tumor-discriminative biomarker candidates which can serve as therapeutic targets for the treatment of ccRCC. IMPLICATIONS: Our in-depth quantitative proteomics analysis of ccRCC tissues identifies the putatively secreted protein SPARC as a promising urine biomarker and reveals two molecular tumor phenotypes.

Comprehensive analysis of prognostic value and immune infiltration of kindlin family members in non-small cell lung cancer

BACKGROUND

Kindlin Family Members have been reported to be aberrantly expressed in various human cancer types and involved in tumorigenesis, tumor progression, and chemoresistance. However, their roles in non-small cell lung cancer (NSCLC) remain poorly elucidated.

METHODS

We analyzed the prognostic value and immune infiltration of Kindlins in NSCLC through Oncomine, GEPIA, UALCAN, CCLE, Kaplan‑Meier plotter, cBioPortal, TIMER, GeneMANIA, STRING, and DAVID database. Additionally, the mRNA expression levels of Kindlins were verified in 30 paired NSCLC tissues and NSCLC cell lines by real-time PCR.

RESULTS

The expression level of FERMT1 was remarkably increased in NSCLC tissues and NSCLC cell lines, while FERMT2 and FERMT3 were reduced. Kindlins expressions were associated with individual cancer stages and nodal metastasis. We also found that higher expression level of FERMT1 was obviously correlated with worse overall survival (OS) in patients with NSCLC, while higher FERMT2 was strongly associated with better overall survival (OS) and first progression (FP). Additionally, the expression of FERMT2 and FERMT3 were obviously correlated with the immune infiltration of diverse immune cells. Functional enrichment analysis has shown that Kindlins may be significantly correlated with intracellular signal transduction, ATP binding and the PI3K-Akt signaling pathway in NSCLC.

CONCLUSIONS

The research provides a new perspective on the distinct roles of Kindlins in NSCLC and likely has important implications for future novel biomarkers and therapeutic targets in NSCLC.

Kindlins as modulators of breast cancer progression

Kindlin-1 (K1, FERMT1), Kindlin-2 (K2, FERMT2), and Kindlin-3 (K3, FERMT3) are the three members of the kindlin family of adapter proteins found in mammals. One or more kindlins are found in most cell types, K1 primarily in epithelial cells, K3 in primarily hematopoietic cells and also endothelial cells, and K2 is very broadly distributed. The kindlins consist primarily of a 4.1-erzin-radixin-moiesin (FERM) domain, which is transected by a lipid-binding plextrin-homology (PH) domain. Deficiencies of each kindlin in mice and/ or humans have profound pathogenic consequences. The most well-established function of kindlins depends on their ability to participate in the activat integrin adhesion receptors. This function depends on the binding of each kindlin to the beta subunit of integrins where it cooperates with talin to enhance avidity of interactions with cognate extracellular matrix ligands. Deficiencies of many different integrins are lethal, are critical for normal development of mammary tissue, and excessive expression and/or activation of certain integrins are associated with progression and metastasis of breast cancer. However, via its interaction with many other intracellular proteins, kindlins can influence numerous cellular responses. Changes in expression of each of the three kindlins have been reported in association with breast cancer, with several studies indicating that kindlins are among the most upregulated genes in breast cancer. The association of abnormal functions of K2 with breast cancer is particularly extensive with many reports indicating that it is a major driver of breast cancer via its promotion of cancer cell proliferation, survival, adhesion, migration, invasion, the epithelial-to-mesenchymal transition and its influence on macrophage recruitment and phenotype. These associations suggest that the kindlins and their functions represent an intriguing therapeutic target for exploration of breast cancer therapy.

Structural basis of human full-length kindlin-3 homotrimer in an auto-inhibited state

Kindlin-1, -2, and -3 directly bind integrin β cytoplasmic tails to regulate integrin activation and signaling. Despite their functional significance and links to several diseases, structural information on full-length kindlin proteins remains unknown. Here, we report the crystal structure of human full-length kindlin-3, which reveals a novel homotrimer state. Unlike kindlin-3 monomer, which is the major population in insect and mammalian cell expression systems, kindlin-3 trimer does not bind integrin β cytoplasmic tail as the integrin-binding pocket in the F3 subdomain of 1 protomer is occluded by the pleckstrin homology (PH) domain of another protomer, suggesting that kindlin-3 is auto-inhibited upon trimer formation. This is also supported by functional assays in which kindlin-3 knockout K562 erythroleukemia cells reconstituted with the mutant kindlin-3 containing trimer-disrupting mutations exhibited an increase in integrin-mediated adhesion and spreading on fibronectin compared with those reconstituted with wild-type kindlin-3. Taken together, our findings reveal a novel mechanism of kindlin auto-inhibition that involves its homotrimer formation.

The crystal structure of a human full-length kindlin protein (kindlin-3) reveals a homotrimeric complex; together with in vitro and in vivo data, this suggests an auto-inhibition model for kindlins in integrin activation.

miR-4792 Inhibits Acute Myeloid Leukemia Cell Proliferation and Invasion and Promotes Cell Apoptosis by Targeting Kindlin-3

It has been reported that kindlin-3 expression is closely associated with progression of many cancers and microRNA (miRNA) processing. However, the effects and precise mechanisms of kindlin-3 in acute myeloid leukemia (AML) have not been well clarified. Our study aimed to explore the interaction between kindlin-3 and miR-4792 in AML. In our study, we found that the expression of kindlin-3 was dramatically increased in AML samples and cell lines, and the miR-4792 level was significantly downregulated. Interestingly, the low miR-4792 level was closely associated with upregulated kindlin-3 expression in AML samples. Moreover, introduction of miR-4792 dramatically suppressed proliferation and invasion and induced apoptosis of AML cells. We demonstrated that miR-4792 could directly target kindlin-3 by using both bioinformatics analysis and luciferase reporter assay. In addition, kindlin-3 silencing had similar effects with miR-4792 overexpression on AML cells. Overexpression of kindlin-3 in AML cells partially reversed the inhibitory effects of miR-4792 mimic. miR-4792 inhibited cell proliferation and invasion and induced apoptosis of AML cells by directly downregulating kindlin-3 expression, and miR-4792 targeting kindlin-3 was responsible for the regulation of the proliferation, invasion, and apoptosis of AML cells.

Site-specific phosphorylation regulates the functions of kindlin-3 in a variety of cells

Studies of isolated cells, mice, and humans have demonstrated the vital role of the FERM domain protein kindlin-3 in integrin activation in certain hematopoietic and non-hematopoietic cells, consequent to binding to integrin β-subunits. To explore regulatory mechanisms, we developed a monoclonal antibody that selectively recognizes the phosphorylated form of Ser⁴⁸⁴ (pS⁴⁸⁴) in kindlin-3. Activation of platelets, HEL megakaryocytic-like cells and BT549 breast cancer cells led to enhanced expression of pS⁴⁸⁴ as assessed by immunofluorescence or Western blotting. In platelets, pS⁴⁸⁴ rose rapidly and transiently upon stimulation. When a mutant form of kindlin-3, T⁴⁸²S⁴⁸⁴/AA kindlin-3, was transduced into mouse megakaryocytes, it failed to support activation of integrin α_IIbβ₃, whereas wild-type kindlin-3 did. In MDA-MB231 breast cancer cells, expression of T⁴⁸²S⁴⁸⁴/AA kindlin-3 suppressed cell spreading, migration, invasion, and VEGF production. Wild-type kindlin-3 expressing cells markedly increased tumor growth in vivo, whereas T⁴⁸²S⁴⁸⁴/AA kindlin-3 significantly blunted tumor progression. Thus, our data establish that a unique phosphorylation event in kindlin-3 regulates its cellular functions.

CD147 Is a Promising Target of Tumor Progression and a Prognostic Biomarker

Microenvironment plays a crucial role in tumor development and progression. Cancer cells modulate the tumor microenvironment, which also contribute to resistance to therapy. Identifying biomarkers involved in tumorigenesis and cancer progression represents a great challenge for cancer diagnosis and therapeutic strategy development. CD147 is a glycoprotein involved in the regulation of the tumor microenvironment and cancer progression by several mechanisms—in particular, by the control of glycolysis and also by its well-known ability to induce proteinases leading to matrix degradation, tumor cell invasion, metastasis and angiogenesis. Accumulating evidence has demonstrated the role of CD147 expression in tumor progression and prognosis, suggesting it as a relevant tumor biomarker for cancer diagnosis and prognosis, as well as validating its potential as a promising therapeutic target in cancers.

Comparative Analysis of the Transcriptome and Proteome during Mouse Placental Development

The condition of the placenta is a determinant of the short- and long-term health of the mother and the fetus. However, critical processes occurring in early placental development, such as trophoblast invasion and establishment of placental metabolism, remain poorly understood. To gain a better understanding of the genes involved in regulating these processes, we utilized a multiomics approach, incorporating transcriptome, proteome, and phosphoproteome data generated from mouse placental tissue collected at two critical developmental time points. We found that incorporating information from both the transcriptome and proteome identifies genes associated with time point-specific biological processes, unlike using the proteome alone. We further inferred genes upregulated on the basis of the proteome data but not the transcriptome data at each time point, leading us to identify 27 genes that we predict to have a role in trophoblast migration or placental metabolism. Finally, using the phosphoproteome data set, we discovered novel phosphosites that may play crucial roles in the regulation of placental transcription factors. By generating the largest proteome and phosphoproteome data sets in the developing placenta, and integrating transcriptome analysis, we uncovered novel aspects of placental gene regulation.

Distinct expression profiles and functions of Kindlins in breast cancer

Background

Kindlin-1, − 2, and − 3 are the three members of the Kindlin family. They are best known as regulators of integrin functions, contributing to fundamental biological processes such as cell survival, adhesion and migration. Their deregulation leads to diverse pathologies including a broad range of cancers in which both, tumor-promoting and tumor-inhibiting functions have been described.

Methods

To better characterize Kindlins implication in breast cancer, in vitro experiments were performed in a series of cancer cell lines. We first assessed their expression profiles and subcellular distributions. Then, their involvement in breast cancer cell morphology, migration and invasion was verified by examining phenotypic changes induced by the depletion of either isoforms using RNA interference. An expression study was performed in a series of breast cancer patient derived xenografts (n = 58) to define the epithelial and stromal contribution of each Kindlin. Finally, we analyzed the expression levels of the three Kindlins in a large series of human breast tumors, at the RNA (n = 438) and protein (n = 129) levels and we evaluated their correlation with the clinical outcome.

Results

We determined that Kindlin-1 and Kindlin-2, but not Kindlin-3, were expressed in breast tumor cells. We uncovered the compensatory roles of Kindlin-1 and -2 in focal adhesion dynamics and cell motility. Remarkably, Kindlin-2 had a predominant effect on cell spreading and Kindlin-1 on cell invasion. In line with these experimental observations, Kindlin-1 overexpression was associated with a worse patients’ outcome. Notably, Kindlin-3, expressed by tumor infiltrating leukocytes, also correlated with a poor prognosis of breast cancer patients.

Conclusion

This study demonstrates that each one of the Kindlin family members has a different expression profile emphasizing their redundant and complementary roles in breast tumor cells. We highlight the specific link between Kindlin-1 and breast cancer progression. In addition, Kindlin-3 overexpression in the tumor microenvironment is associated with more aggressive breast tumors.

These results suggest that Kindlins play distinctive roles in breast cancer. Kindlins may be useful in identifying breast cancer patients with a worst prognosis and may offer new avenues for therapeutic intervention against cancer progression.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0955-4) contains supplementary material, which is available to authorized users.

Prognostic value of NUSAP1 in progression and expansion of glioblastoma multiforme

Nucleolar and spindle-associated protein (NUSAP1) is a microtubule and chromatin-binding protein that stabilizes microtubules to prevent depolymerization, maintains spindle integrity. NUSAP1 could cross-link spindles into aster-like structures, networks and fibers. It has also been found to play roles in progression of several cancers. However, the potential correlation between NUSAP1 and clinical outcome in patients with glioblastoma multiforme (GBM) remains largely unknown. In the current study, we demonstrated that NUSAP1 was significantly up-regulated in GBM tissues compared with adult non-tumor brain tissues both in a validated cohort and a TCGA cohort. In addition, Kaplan-Meier analysis indicated that patients with high NUSAP1 expression had significantly lower OS (P = 0.0027). Additionally, in the TCGA cohort, NUSAP1 expression was relatively lower in GBM patients within the neural and mesenchymal subtypes compared to other subtypes, and associated with the status of several genetic aberrations such as PTEN deletion and wild type IDH1. The present study provides new insights and evidence that NUSAP1 over-expression was significantly correlated with progression and prognosis of GBM. Furthermore, knockdown of NUSAP1 revealed its regulation on G2/M progression and cell proliferation (both in vitro and in vivo). These data demonstrate that NUSAP1 could serve as a novel prognostic biomarker and a potential therapeutic target for GBM.

Kindlins: Roles in development and cancer progression

The Kindlins are FERM domain proteins comprising three members (Kindlin-1, -2 and -3) which are evolutionarily conserved. Kindlins bind with β-integrin cytoplasmic tails and execute broad biological functions including directed cell migration, proliferation, differentiation and survival. In light of more and more evidence point to the importance of Kindlin family members in normal development and human diseases especially in cancers, we aim to portrait the profile of Kindlins in the regulation of embryonic development and cancer progression. We first summarize all the known binding proteins for individual member of Kindlin family. We then outline the Kindlin-regulated signaling pathways including Wnt/β-catenin, TGFβ, EGFR, and Hedgehog signalings. Furthermore, we descript the pivotal role of Kindlins in embryonic development in detail with notions that Kindlin-1 is highly expressed in endo/ectodermal originated tissues, Kindlin-2 is highly expressed in mesoderm-derived tissues and Kindlin-3 is highly expressed in mesoderm- and ectoderm-derived tissues. Deregulation of Kindlins is generally reported in cancers from different organs. We also briefly descript the role of Kindlins in other diseases. Finally, we update the recent understanding of how Kindlins are regulated and modified as well as the degradation mechanism of Kindlins, respectively.

FERMT3 contributes to glioblastoma cell proliferation and chemoresistance to temozolomide through integrin mediated Wnt signaling

FERMT3, also known as kindlin-3, is one of three kindlin family members expressed in mammals. Kindlins are cytosolic, adaptor proteins that are important activators and regulators of integrin function. They have also been shown to play critical roles in the development and progression of various cancers. In the present study, we hypothesized that FERMT3 would enhance glioblastoma multiforme (GBM) cell survival. Indeed, expression level analyses showed significant FERMT3 upregulation in human glioma tissues as compared to normal brain tissues. The effect was particularly pronounced in high-grade gliomas. We then demonstrated that FERMT3 knockdown suppresses glioma cell proliferation and chemoresistance to temozolomide (TMZ). To determine the mechanism by which FERMT3 enhances glioma cell proliferation and chemoresistance, we examined the effects of FERMT3 on integrin activation and Wnt/β-catenin signaling. Through the use of western blot assays and TOPflash and FOPflash plasmid transfection into glioma cells lines, we demonstrated that FERMT3 regulates glioma cell activity through integrin-mediated Wnt/β-catenin signaling. These results suggest that FERMT3 activates integrin activity in high-grade gliomas to enhance glioma cell survival and chemoresistance. The present study thus indicates a potential role for FERMT3 as a genetic target in the treatment of GBM.

Prognostic implications of Kindlin proteins in human osteosarcoma

The Kindlin protein family, comprising Kindlin-1, Kindlin-2 and Kindlin-3, play important roles in various human cancers. Here, to explore the clinical significance of Kindlins in human osteosarcomas, quantitative real-time PCR and Western blot analyses were performed to detect the expression of Kindlin-1, Kindlin-2 and Kindlin-3 mRNAs and proteins in 20 self-pairs of osteosarcoma and adjacent noncancerous tissues. Then, immunohistochemistry was performed to examine subcellular localizations and expression patterns of Kindlin proteins in 100 osteosarcoma and matched adjacent noncancerous tissues. Kindlin-1, Kindlin-2 and Kindlin-3 protein immunostainings were localized in the cytoplasm, nucleus and cytoplasm, respectively, of tumor cells in primary osteosarcoma tissues. Statistically, the expression levels of Kindlin-1 and Kindlin-2 mRNAs and proteins in osteosarcoma tissues were all significantly higher (both P<0.01), but those of Kindlin-3 mRNA and protein were both dramatically lower (both P<0.05), than in matched adjacent noncancerous tissues. In addition, the overexpressions of Kindlin-1 and Kindlin-2 proteins were both significantly associated with high tumor grade (both P=0.01), presence of metastasis (both P=0.006), recurrence (both P=0.006) and poor response to chemotherapy (both P=0.02). Moreover, Kindlin-1 and Kindlin-2 expressions were both identified as independent prognostic factors for overall (both P=0.01) and disease-free (P=0.02 and 0.01, respectively) survivals of osteosarcoma patients. However, no associations were observed between Kindlin-3 expression and various clinicopathologic features and patients’ prognosis. In conclusion, aberrant expression of Kindlin-1 and Kindlin-2 may function as reliable markers for progression and prognosis in osteosarcoma patients, especially for tumor recurrence.

Expression of kindlin-3 in melanoma cells impedes cell migration and metastasis

Kindlins are a small family of 4.1-ezrin-radixin-moesin (FERM)-containing cytoplasmic proteins. Kindlin-3 is expressed in platelets, hematopoietic cells, and endothelial cells. Kindlin-3 promotes integrin activation, clustering and outside-in signaling. Aberrant expression of kindlin-3 was reported in melanoma and breast cancer. Intriguingly, kindlin-3 has been reported to either positively or negatively regulate cancer cell metastasis. In this study, we sought to clarify the expression of kindlin-3 in melanoma cells and its role in melanoma metastasis. Two widely used metastatic mouse and human melanoma cell lines B16-F10 and M10, respectively, were examined and found to lack kindlin-3 mRNA and protein expression. When kindlin-3 was ectopically expressed in these cells, cell migration was markedly reduced. These are attributed to aberrant Rac1 and RhoA activation and overt membrane ruffling. Our data demonstrate for the first time that despite its well established role as a positive regulator of integrin-mediated cell adhesion, aberrant expression of kindlin-3 could lead to imbalanced RhoGTPases signaling that impedes rather than promotes cell migration.

The kindlin family: functions, signaling properties and implications for human disease

The kindlin (or fermitin) family of proteins comprises three members (kindlin-1,-2 and -3) of evolutionarily conserved focal adhesion (FA) proteins, whose best-known task is to increase integrin affinity for a ligand (also referred as integrin activation) through binding of β-integrin tails. The consequence of kindlin-mediated integrin activation and integrin-ligand binding is cell adhesion, spreading and migration, assembly of the extracellular matrix (ECM), cell survival, proliferation and differentiation. Another hallmark of kindlins is their involvement in disease. Mutations in the KINDLIN-1 (also known as FERMT1) gene cause Kindler syndrome (KS)--in which mainly skin and intestine are affected, whereas mutations in the KINDLIN-3 (also known as FERMT3) gene cause leukocyte adhesion deficiency type III (LAD III), which is characterized by impaired extravasation of blood effector cells and severe, spontaneous bleedings. Also, aberrant expression of kindlins in various forms of cancer and in tissue fibrosis has been reported. Although the malfunctioning of integrins represent a major cause leading to kindlin-associated diseases, increasing evidence also point to integrin-independent functions of kindlins that play an important role in the pathogenesis of certain disease aspects. Furthermore, isoform-specific kindlin functions have been discovered, explaining, for example, why loss of kindlins differentially affects tissue stem cell homeostasis or tumor development. This Commentary focuses on new and isoform-specific kindlin functions in different tissues and discusses their potential role in disease development and progression.

Of Kindlins and Cancer

Kindlins are 4.1-ezrin-ridixin-moesin (FERM) domain containing proteins. There are three kindlins in mammals, which share high sequence identity. Kindlin-1 is expressed primarily in epithelial cells, kindlin-2 is widely distributed and is particularly abundant in adherent cells, and kindlin-3 is expressed primarily in hematopoietic cells. These distributions are not exclusive; some cells express multiple kindlins, and transformed cells often exhibit aberrant expression, both in the isoforms and the levels of kindlins. Great interest in the kindlins has emerged from the recognition that they play major roles in controlling integrin function. In vitro studies, in vivo studies of mice deficient in kindlins, and studies of patients with genetic deficiencies of kindlins have clearly established that they regulate the capacity of integrins to mediate their functions. Kindlins are adaptor proteins; their function emanate from their interaction with binding partners, including the cytoplasmic tails of integrins and components of the actin cytoskeleton. The purpose of this review is to provide a brief overview of kindlin structure and function, a consideration of their binding partners, and then to focus on the relationship of each kindlin family member with cancer. In view of many correlations of kindlin expression levels and neoplasia and the known association of integrins with tumor progression and metastasis, we consider whether regulation of kindlins or their function would be attractive targets for treatment of cancer.

NMR Characterization and Membrane Interactions of the Loop Region of Kindlin-3 F1 Subdomain

Kindlins-1,2 and 3 are FERM domain-containing cytosolic proteins involved in the activation and regulation of integrin-mediated cell adhesion. Apart from binding to integrin β cytosolic tails, kindlins and the well characterized integrin-activator talin bind membrane phospholipids. The ubiquitin-like F1 sub-domain of the FERM domain of talin contains a short loop that binds to the lipid membrane. By contrast, the F1 sub-domain of kindlins contains a long loop demonstrated binding to the membrane. Here, we report structural characterization and lipid interactions of the 83-residue F1 loop of kindlin-3 using NMR and optical spectroscopy methods. NMR studies demonstrated that the F1 loop of kindlin-3 is globally unfolded but stretches of residues assuming transient helical conformations could be detected in aqueous solution. We mapped membrane binding interactions of the F1 loop with small unilamellar vesicles (SUVs) containing either zwitterionic lipids or negatively charged lipids using 15N-1H HSQC titrations. These experiments revealed that the F1 loop of kindlin-3 preferentially interacted with the negatively charged SUVs employing almost all of the residues. By contrast, only fewer residues appeared to be interacted with SUVs containing neutral lipids. Further, CD and NMR data suggested stabilization of helical conformations and predominant resonance perturbations of the F1 loop in detergent containing solutions. Conformations of an isolated N-terminal peptide fragment, or EK21, of the F1 loop, containing a poly-Lys sequence motif, important for membrane interactions, were also investigated in detergent solutions. EK21 adopted a rather extended or β-type conformations in complex with negatively charged SDS micelles. To our knowledge, this is the first report describing the conformations and residue-specific interactions of kindlin F1 loop with lipids. These data therefore provide important insights into the interactions of kindlin FERM domain with membrane lipids that contribute toward the integrin activating property.

High expression of N-myc (and STAT) interactor predicts poor prognosis and promotes tumor growth in human glioblastoma

Glioma is the most malignant brain tumor and glioblastoma (GBM) is the most aggressive type. The involvement of N-myc (and STAT) interactor (NMI) in tumorigenesis was sporadically reported but far from elucidation. This study aims to investigate roles of NMI in human glioma. Three independent cohorts, the Chinese tissue microarray (TMA) cohort (N = 209), the Repository for Molecular Brain Neoplasia Data (Rembrandt) cohort (N = 371) and The Cancer Genome Atlas (TCGA) cohort (N = 528 or 396) were employed. Transcriptional or protein levels of NMI expression were significantly increased according to tumor grade in all three cohorts. High expression of NMI predicted significantly unfavorable clinical outcome for GBM patients, which was further determined as an independent prognostic factor. Additionally, expression and prognostic value of NMI were associated with molecular features of GBM including PTEN deletion and EGFR amplification in TCGA cohort. Furthermore, overexpression or depletion of NMI revealed its regulation on G1/S progression and cell proliferation (both in vitro and in vivo), and this effect was partially dependent on STAT1, which interacted with and was regulated by NMI. These data demonstrate that NMI may serve as a novel prognostic biomarker and a potential therapeutic target for glioblastoma.

Kindlin-3 interacts with the ribosome and regulates c-Myc expression required for proliferation of chronic myeloid leukemia cells

Kindlins are FERM-containing cytoplasmic proteins that regulate integrin-mediated cell-cell and cell-extracellular matrix (ECM) attachments. Kindlin-3 is expressed in hematopoietic cells, platelets, and endothelial cells. Studies have shown that kindlin-3 stabilizes cell adhesion mediated by ß1, ß2, and ß3 integrins. Apart from integrin cytoplasmic tails, kindlins are known to interact with other cytoplasmic proteins. Here we demonstrate that kindlin-3 can associate with ribosome via the receptor for activated-C kinase 1 (RACK1) scaffold protein based on immunoprecipitation, ribosome binding, and proximity ligation assays. We show that kindlin-3 regulates c-Myc protein expression in the human chronic myeloid leukemia cell line K562. Cell proliferation was reduced following siRNA reduction of kindlin-3 expression and a significant reduction in tumor mass was observed in xenograft experiments. Mechanistically, kindlin-3 is involved in integrin α5ß1-Akt-mTOR-p70S6K signaling; however, its regulation of c-Myc protein expression could be independent of this signaling axis.