Opposite Role of Kindlin-1 and Kindlin-2 in Lung Cancers

Lung cancer is highly heterogenous and is composed of various subtypes that are in diverse differential stages. The newly identified integrin-interacting proteins Kindlin-1 and Kindlin-2 are the activators of transmembrane receptor integrins that play important roles in cancer progression. In this report we present the expression profiles of Kindlin-1 and Kindlin-2 in lung cancers using patient specimens and established their correlation with lung cancer progression. We found that Kindlin-1 was expressed in epithelia-derived non-small-cell lung cancer, especially in squamous cell lung cancer but expressed at low levels in poorly differentiated large cell lung cancer. However, Kindlin-2 was highly expressed in large cell lung cancer. Both Kindlin-1 and Kindlin-2 were found not expressed or expressed at very low levels in neuroendocrine-derived small cell lung cancer. Importantly, the Kindlin-1 expression level was positively correlated with the differentiation of squamous cell lung cancer. Surprisingly, we found that the very homologous Kindlin family proteins, Kindlin-1 and Kindlin-2, displayed counteracting functional roles in lung cancer cells. Ectopic expression of Kindlin-1 in non-small-cell lung cancer cells inhibited in vitro cell migration and in vivo tumor growth, while Kindlin-2 promoted these functions. Mechanistically, Kindlin-1 prohibited epithelail to mesenchymal transition in non-small-cell lung cancer cells, while Kindlin-2 enhanced epithelail to mesenchymal transition in these cells. Taken together, we demonstrated that Kindlin-1 and Kindlin-2 differentially regulate lung cancer cell progression. Further, the expression levels of Kindlin-1 might be potentially used as a marker for lung cancer differentiation and targeting Kindlin-2 might block the invasive growth of large cell lung cancer.     

Integrin-interacting protein Kindlin-2 induces mammary tumors in transgenic mice

Kindlin-2, an integrin-interacting protein, regulates breast cancer progression. However, currently, no animal model to study the role of Kindlin-2 in the carcinogenesis of mammary gland is available. We established a Kindlin-2 transgenic mouse model using a mammary gland-specific promoter, mammary tumor virus (MMTV) long terminal repeat (LTR). Kindlin-2 was overexpressed in the epithelial cells of the transgenic mice. The mammary gland ductal trees were found to grow faster in MMTV-Kindlin-2 transgenic mice than in control mice during puberty. Kindlin-2 promoted mammary gland growth as indicated by more numerous duct branches and larger lumens, and more alveoli were formed in the mammary glands during pregnancy under Kindlin-2 overexpression. Importantly, mammary gland-specific expression of Kindlin-2 induced tumor formation at the age of 55 weeks on average. Additionally, the levels of estrogen receptor and progesterone receptor were decreased, whereas human epidermal growth factor receptor 2 and β-catenin were upregulated in the Kindlin-2-induced mammary tumors. These findings demonstrated that Kindlin-2 induces mammary tumor formation via activation of the Wnt signaling pathway.

     

Simulations of Kindlin-2 PIP binding domains reveal protonation-dependent membrane binding modes

Kindlin-2, a member of the Kindlin family of peripheral membrane proteins, is important for integrin activation and stabilization of epidermal growth factor receptor. It associates with the cytoplasmic face of the plasma membrane via dedicated phosphatidylinositol phosphate binding domains located in the N-terminal F0 and Pleckstrin Homology domains. These domains have binding affinity for phosphatidylinositol 4,5-bisphosphate and, to a greater degree, phosphatidylinositol 3,4,5-trisphosphate. The biological significance of the differential binding of these phosphatidylinositol phosphates to Kindlin-2 and the mechanism by which they activate Kindlin-2 are not well understood. Recently, ssNMR identified the predominant protonation states of phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate near physiological pH in the presence of anionic lipids. Here, we perform atomistic simulation of the bound state of the Pleckstrin Homology and F0 domains of Kindlin-2 at membranes containing phosphatidylinositol 4,5-bisphosphate/phosphatidylinositol 3,4,5-trisphosphate with differing protonation states. This computational approach demonstrates that these two phosphatidylinositol phosphates differently modulate Kindlin-2 subdomain binding in a protonation-state-dependent manner. We speculate these variations in binding mode provide a mechanism for intracellular pH and Ca²⁺ influx to control the membrane binding behavior and activity of Kindlin-2.     

Kindlin-2 expression in adult tissues correlates with their embryonic origins

Kindlin-2 functions in the maintenance of homeostasis and in human diseases. This study investigated the interrelationship between Kindlin-2 expression in tissues and the corresponding germ layers from which these tissues originated. Kindlin-2 expression was examined in normal adult human organs and human cancer tissues by immunohistochemical analyses. Analysis of Kindlin-2 mRNA levels in adult human organs in the Oncomine dataset revealed Kindlin-2 is highly expressed in mesoderm-derived organs. However, Kindlin-2 was negative or weakly expressed in endoderm/ectoderm-derived organs. Interestingly, the abnormal expression of Kindlin-2 was observed in a variety of human cancers. In agreement with its expression profile in humans, Kindlin-2 was also highly expressed in mesoderm-derived organs in mouse embryos with the exception of strong Kindlin-2 expression in ectoderm-derived spinal cord and ganglia, tissues that are highly mobile during embryonic development. Importantly, we demonstrated the expression level of Kindlin-2 in adult organs correlated with their embryonic dermal origins and deregulation of Kindlin-2 in tissues is associated with tumor progression. This finding will help us understand the dual role of Kindlin-2 in the regulation of tumor progression and embryonic development.     

Differential expression of Kindlin-1 and Kindlin-2 correlates with esophageal cancer progression and epidemiology

Esophageal cancer(EC) is one of the most lethal malignancies in China, but the etiology and risk factors remain unclear.The integrin-interacting proteins Kindlin-1 and Kindlin-2 are focal adhesion molecules that activate transmembrane receptor integrins and regulate tumor cell growth, invasion, and metastasis. Here, we report that Kindlin-I and Kindlin-2 are differentially expressed among Chinese EC patients. For this, Kindlin-1 and Kindlin-2 expression was evaluated in 220 EC patients by immunohistochemistry(IHC) and found to be correlated with the EC progression, along with a variety of epidemiologic parameters,including smoking,family EC history,and EC invasion status. Moreover,data downloaded from the Oncomine database revealed that both Kindlin-1 and Kindlin-2 were upregulated in ECs compared with normal esophageal tissues; although Kindlin-1 was highly expressed in well-differentiated tumors, whereas Kindlin-2 was more prevalent in poorly differentiated tumors. Collectively, these data suggest that Kindlin-1 may inhibit, while Kindlin-2 may promote, EC progression. This study,for the first time, linked the expression of Kindlin-1 and Kindlin-2 with EC family genetic background and living habits, which may help further our understanding of the various causes of EC.     

Biophysical Analysis of Kindlin-3 Reveals an Elongated Conformation and Maps Integrin Binding to the Membrane-distal ��-Subunit NPXY Motif

Kindlin-3, a 75-kDa protein, has been shown to be critical for hemostasis, immunity, and bone metabolism via its role in integrin activation. The Kindlin family is hallmarked by a FERM domain comprised of F1, F2, and F3 subdomains together with an N-terminal F0 domain and a pleckstrin homology domain inserted in the F2 domain. Recombinant Kindlin-3 was cloned, expressed, and purified, and its domain organization was studied by x-ray scattering and other techniques to reveal an extended conformation. This unusual elongated structure is similar to that found in the paralogue Talin head domain. Analytical ultracentrifugation experiments indicated that Kindlin-3 forms a ternary complex with the Talin and β-integrin cytoplasmic tails. NMR showed that Kindlin-3 specifically recognizes the membrane-distal tail NPXY motif in both the β_1A and β_1D isoforms, although the interaction is stronger with β_1A. An upstream Ser/Thr cluster in the tails also plays a critical role. Overall these data support current biological, clinical, and mutational data on Kindlin-3/β-tail binding and provide novel insights into the overall conformation and interactions of Kindlin-3.     

Kindlin-2 promotes Src-mediated tyrosine phosphorylation of androgen receptor and contributes to breast cancer progression

Androgen receptor (AR) signaling plays important roles in breast cancer progression. We show here that Kindlin-2, a focal adhesion protein, is critically involved in the promotion of AR signaling and breast cancer progression. Kindlin-2 physically associates with AR and Src through its two neighboring domains, namely F1 and F0 domains, resulting in formation of a Kindlin-2-AR-Src supramolecular complex and consequently facilitating Src-mediated AR Tyr-534 phosphorylation and signaling. Depletion of Kindlin-2 was sufficient to suppress Src-mediated AR Tyr-534 phosphorylation and signaling, resulting in diminished breast cancer cell proliferation and migration. Re-expression of wild-type Kindlin-2, but not AR-binding-defective or Src-binding-defective mutant forms of Kindlin-2, in Kindlin-2-deficient cells restored AR Tyr-534 phosphorylation, signaling, breast cancer cell proliferation and migration. Furthermore, re-introduction of phosphor-mimic mutant AR-Y534D, but not wild-type AR reversed Kindlin-2 deficiency-induced inhibition of AR signaling and breast cancer progression. Finally, using a genetic knockout strategy, we show that ablation of Kindlin-2 from mammary tumors in mouse significantly reduced AR Tyr-534 phosphorylation, breast tumor progression and metastasis in vivo. Our results suggest a critical role of Kindlin-2 in promoting breast cancer progression and shed light on the molecular mechanism through which it functions in this process.Subject terms: Cell signalling, Breast cancer     

Depletion of Kindlin-2 induces cardiac dysfunction in mice

Kindlin-2, a member of the Kindlin family focal adhesion proteins, plays an important role in cardiac development. It is known that defects in the Z-disc proteins lead to hypertrophic cardiomyopathy (HCM) or dilated cardiomyopathy (DCM). Our previous investigation showed that Kindlin-2 is mainly localized at the Z-disc and depletion of Kindlin-2 disrupts the structure of the Z-Disc. Here, we reported that depletion of Kindlin-2 leads to the disordered myocardial fibers, fractured and vacuolar degeneration in myocardial fibers. Interestingly, depletion of Kindlin-2 in mice induced cardiac myocyte hypertrophy and increased the heart weight. Furthermore, decreased expression of Kindlin-2 led to cardiac dysfunction and also markedly impairs systolic function. Our data indicated that Kindlin-2 not only maintains the cardiac structure but also is required for cardiac function.     

Kindlin-2 in Sertoli cells is essential for testis development and male fertility in mice

Kindlin-2 is known to play important roles in the development of mesoderm-derived tissues including myocardium, smooth muscle, cartilage and blood vessels. However, nothing is known for the role of Kindlin-2 in mesoderm-derived reproductive organs. Here, we report that loss of Kindlin-2 in Sertoli cells caused severe testis hypoplasia, abnormal germ cell development and complete infertility in male mice. Functionally, loss of Kindlin-2 inhibits proliferation, increases apoptosis, impairs phagocytosis in Sertoli cells and destroyed the integration of blood-testis barrier structure in testes. Mechanistically, Kindlin-2 interacts with LATS1 and YAP, the key components of Hippo pathway. Kindlin-2 impedes LATS1 interaction with YAP, and depletion of Kindlin-2 enhances LATS1 interaction with YAP, increases YAP phosphorylation and decreases its nuclear translocation. For clinical relevance, lower Kindlin-2 expression and decreased nucleus localization of YAP was found in SCOS patients. Collectively, we demonstrated that Kindlin-2 in Sertoli cells is essential for sperm development and male reproduction.Subject terms: Apoptosis, Male factor infertility     

Kindler syndrome protein Kindlin-1 is mainly expressed in adult tissues originating from ectoderm/endoderm

Mutations of integrin-interacting protein Kindlin-1 cause Kindler syndrome and deregulation of Kindlin-1 is implicated in human cancers. The Kindlin-1-related diseases are confined in limited tissue types. However, Kindlin-1 tissue distribution and the dogma that governs Kindlin-1 expression in normal human body are elusive. This study examined Kindlin-1 expression in normal human adult organs, human and mouse embryonic organs by immunohistochemical analyses. We identified a general principle that the level of Kindlin-1 expression in tissues is tightly correlated with the corresponding germ layers from which these tissues originate. We compared the expression of Kindlin-1 with Kindlin-2 and found that Kindlin-1 is highly expressed in epithelial tissues derived from ectoderm and endoderm, whereas Kindlin-2 is mainly expressed in mesoderm-derived tissues. Likewise, Kindlin-1 was also found highly expressed in endoderm/ectoderm-derived tissues in human and mouse embryos. Our findings indicate that Kindlin-1 may play an importance role in the development of endoderm/ectoderm related tissues.     

Identification of a leader exon and a core promoter for the rat tuberous sclerosis 2 (Tsc2) gene and structural comparison with the human homolog

Hereditary renal carcinoma in the Eker rat is an excellent example of predisposition to a specific cancer being transmitted as a dominant trait. Recently, we identified a germline mutation of the tuberous sclerosis 2 (Tsc2) gene in the Eker rat. In the present study, we analyzed the upstream region of the Tsc2 gene. A novel leader exon (exon 1a) in a CpG island was found, and core promoter activity was identified in a 242-bp region of this island. Exon 1a and the promoter region were conserved in the human TSC2 gene. In addition, a rat homolog of a gene found upstream of TSC2 in human has been identified, indicating that the genomic organization around Tsc2/TSC2 is conserved between the two species. Characterization of the 5′ region of Tsc2 and TSC2 will facilitate studies of the regulation of the gene and its disregulation in tumorigenesis. Received: 1 February 1997 / Accepted: 4 April 1997