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

Hematopoietic stem cell transplantation corrects osteopetrosis in a child carrying a novel homozygous mutation in the FERMT3 gene

Osteopetrosis (OPT) is a rare skeletal disorder with phenotypic and genotypic heterogeneity: a variety of clinical features besides the bony defect may be present, and at least ten different genes are known to be involved in the disease pathogenesis. In the framework of this heterogeneity, we report the clinical description of a neonate, first child of consanguineous parents, who had osteoclast-rich osteopetrosis and bone marrow failure in early life, but no other usual classical features of infantile malignant OPT, such as visual or hearing impairments. Because of the severe presentation at birth, the patient received Hematopoietic Stem Cell Transplantation (HSCT) at 2months of age with successful outcome. Post-HSCT genetic investigation by means of exome sequencing identified a novel homozygous mutation in the Fermitin Family Member 3 (FERMT3) gene, which was predicted to disrupt the functionality of its protein product kindlin 3. Our report provides information relevant to physicians for recognizing patients with one of the rarest forms of infantile malignant OPT, and clearly demonstrates that HSCT cures kindlin 3 deficiency with severe phenotype.

Kindlin-2 in pancreatic stellate cells promotes the progression of pancreatic cancer

Pancreatic stellate cells (PSCs) play a pivotal role in pancreatic fibrosis associated with pancreatic ductal adenocarcinoma (PDAC). Kindlin-2 is a focal adhesion protein that regulates the activation of integrins. This study aimed to clarify the role of kindlin-2 in PSCs in pancreatic cancer. Kindlin-2 expression in 79 resected pancreatic cancer tissues was examined by immunohistochemical staining. Kindlin-2-knockdown immortalized human PSCs were established using small interfering RNA. Pancreatic cancer cells were treated with conditioned media of PSCs, and the cell proliferation and migration were examined. SUIT-2 pancreatic cancer cells were subcutaneously injected into nude mice alone or with PSCs and the size of the tumors was monitored. Kindlin-2 expression was observed in PDAC and the peritumoral stroma. Stromal kindlin-2 expression was associated with shorter recurrence-free survival time after R0 resection. Knockdown of kindlin-2 resulted in decreased proliferation, migration, and cytokine expression in PSCs. The PSC-induced proliferation and migration of pancreatic cancer cells were suppressed by kindlin-2 knockdown in PSCs. In vivo, co-injection of PSCs increased the size of the tumors, but this effect was abolished by kindlin-2 knockdown in PSCs. In conclusion, kindlin-2 in PSCs promoted the progression of pancreatic cancer.

Dynamin2 controls Rap1 activation and integrin clustering in human T lymphocyte adhesion

Leukocyte trafficking is crucial to facilitate efficient immune responses. Here, we report that the large GTPase dynamin2, which is generally considered to have a key role in endocytosis and membrane remodeling, is an essential regulator of integrin-dependent human T lymphocyte adhesion and migration. Chemical inhibition or knockdown of dynamin2 expression significantly reduced integrin-dependent T cell adhesion in vitro. This phenotype was not observed when T cells were treated with various chemical inhibitors which abrogate endocytosis or actin polymerization. We furthermore detected dynamin2 in signaling complexes and propose that it controls T cell adhesion via FAK/Pyk2- and RapGEF1-mediated Rap1 activation. In addition, the dynamin2 inhibitor-induced reduction of lymphocyte adhesion can be rescued by Rap1a overexpression. We demonstrate that the dynamin2 effect on T cell adhesion does not involve integrin affinity regulation but instead relies on its ability to modulate integrin valency. Taken together, we suggest a previously unidentified role of dynamin2 in the regulation of integrin-mediated lymphocyte adhesion via a Rap1 signaling pathway.

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.

Kindlin-2 Modulates the Survival, Differentiation, and Migration of Induced Pluripotent Cell-Derived Mesenchymal Stromal Cells

Kindlin-2 is a multidomain intracellular protein that can be recruited to β-integrin domains to activate signaling, initiate transcriptional programs, and bind to E-cadherin. To explore its involvement in cell fate decisions in mesenchymal cells, we studied the effects of Kindlin-2 modification (overexpression/knockdown) in induced pluripotent cell-derived mesenchymal stromal cells (iPSC-MSCs). Kindlin-2 overexpression resulted in increased proliferation and reduced apoptosis of iPSC-MSCs, as well as inhibition of their differentiation towards osteocytes, adipocytes, and chondrocytes. In contrast, siRNA-mediated Kindlin-2 knockdown induced increased apoptosis and increased differentiation response in iPSC-MSCs. The ability of iPSC-MSCs to adhere to VCAM-1/SDF-1α under shear stress and to migrate in a wound scratch assay was significantly increased after Kindlin-2 overexpression. In contrast, inhibition of mixed lymphocyte reaction (MLR) was generally independent of Kindlin-2 modulation in iPSC-MSCs, except for decreased production of interleukin-2 (IL-2) after Kindlin-2 overexpression in iPS-MSCs. Thus, Kindlin-2 upregulates survival, proliferation, stemness, and migration potential in iPSC-MSCs and may therefore be beneficial in optimizing performance of iPSC-MSC in therapies.

Expression of an Activated Integrin Promotes Long-Distance Sensory Axon Regeneration in the Spinal Cord

After CNS injury, axon regeneration is blocked by an inhibitory environment consisting of the highly upregulated tenascin-C and chondroitin sulfate proteoglycans (CSPGs). Tenascin-C promotes growth of axons if they express a tenascin-binding integrin, particularly α9β1. Additionally, integrins can be inactivated by CSPGs, and this inhibition can be overcome by the presence of a β1-binding integrin activator, kindlin-1. We examined the synergistic effect of α9 integrin and kindlin-1 on sensory axon regeneration in adult rat spinal cord after dorsal root crush and adeno-associated virus transgene expression in dorsal root ganglia. After 12 weeks, axons from C6-C7 dorsal root ganglia regenerated through the tenascin-C-rich dorsal root entry zone into the dorsal column up to C1 level and above (>25 mm axon length) through a normal pathway. Animals also showed anatomical and electrophysiological evidence of reconnection to the dorsal horn and behavioral recovery in mechanical pressure, thermal pain, and ladder-walking tasks. Expression of α9 integrin or kindlin-1 alone promoted much less regeneration and recovery.

SIGNIFICANCE STATEMENT

The study demonstrates that long-distance sensory axon regeneration over a normal pathway and with sensory and sensory-motor recovery can be achieved. This was achieved by expressing an integrin that recognizes tenascin-C, one of the components of glial scar tissue, and an integrin activator. This enabled extensive long-distance (>25 mm) regeneration of both myelinated and unmyelinated sensory axons with topographically correct connections in the spinal cord. The extent of growth and recovery we have seen would probably be clinically significant. Restoration of sensation to hands, perineum, and genitalia would be a significant improvement for a spinal cord-injured patient.