Mesenchyme-derived vertebrate lonesome kinase controls lung organogenesis by altering the matrisome

Vertebrate lonesome kinase (VLK) is the only known secreted tyrosine kinase and responsible for the phosphorylation of a broad range of secretory pathway-resident and extracellular matrix proteins. However, its cell-type specific functions in vivo are still largely unknown. Therefore, we generated mice lacking the VLK gene (protein kinase domain containing, cytoplasmic (Pkdcc)) in mesenchymal cells. Most of the homozygous mice died shortly after birth, most likely as a consequence of their lung abnormalities and consequent respiratory failure. E18.5 embryonic lungs showed a reduction of alveolar type II cells, smaller bronchi, and an increased lung tissue density. Global mass spectrometry-based quantitative proteomics identified 97 proteins with significantly and at least 1.5-fold differential abundance between genotypes. Twenty-five of these had been assigned to the extracellular region and 15 to the mouse matrisome. Specifically, fibromodulin and matrilin-4, which are involved in extracellular matrix organization, were significantly more abundant in lungs from Pkdcc knockout embryos. These results support a role for mesenchyme-derived VLK in lung development through regulation of matrix dynamics and the resulting modulation of alveolar epithelial cell differentiation.

The secreted tyrosine kinase VLK is essential for normal platelet activation and thrombus formation

Tyrosine phosphorylation of extracellular proteins is observed in cell cultures and in vivo, but little is known about the functional roles of tyrosine phosphorylation of extracellular proteins. Vertebrate lonesome kinase (VLK) is a broadly expressed secretory pathway tyrosine kinase present in platelet α-granules. It is released from platelets upon activation and phosphorylates substrates extracellularly. Its role in platelet function, however, has not been previously studied. In human platelets, we identified phosphorylated tyrosines mapped to luminal or extracellular domains of transmembrane and secreted proteins implicated in the regulation of platelet activation. To determine the role of VLK in extracellular tyrosine phosphorylation and platelet function, we generated mice with a megakaryocyte/platelet-specific deficiency of VLK. Platelets from these mice are normal in abundance and morphology but have significant changes in function both in vitro and in vivo. Resting and thrombin-stimulated VLK-deficient platelets exhibit a significant decrease in several tyrosine phosphobands. Results of functional testing of VLK-deficient platelets show decreased protease-activated receptor 4-mediated and collagen-mediated platelet aggregation but normal responses to adenosine 5'-diphosphate. Dense granule and α-granule release are reduced in these platelets. Furthermore, VLK-deficient platelets exhibit decreased protease-activated receptor 4-mediated Akt (S473) and Erk1/2 (T202/Y204) phosphorylation, indicating altered proximal signaling. In vivo, mice lacking VLK in megakaryocytes/platelets display strongly reduced platelet accumulation and fibrin formation after laser-induced injury of cremaster arterioles compared with control mice but with normal bleeding times. These studies show that the secretory pathway tyrosine kinase VLK is critical for stimulus-dependent platelet activation and thrombus formation, providing the first evidence that a secreted protein kinase is required for normal platelet function.

Assessing Collagen Deposition During Aging in Mammalian Tissue and in Caenorhabditis elegans

Proper collagen homeostasis is essential for development and aging of any multicellular organism. During aging, two extreme scenarios are commonly occurring: a local excess in collagen deposition, for instance during fibrosis, or a gradual overall reduction of collagen mass. Here, we describe a histological and a colorimetric method to assess collagen levels in mammalian tissues and in the nematode Caenorhabditis elegans. The first method is the polychrome Herovici staining to distinguish between young and mature collagen ratios. The second method is based on hydroxyproline measurements to estimate collagen protein levels. In addition, we show how to decellularize the multicellular organism C. elegans in order to harvest its cuticle, one of the two major extracellular matrices, mainly composed of collagen. These methods allow assessing collagen deposition during aging either in tissues or in whole organisms.

A secreted tyrosine kinase acts in the extracellular environment

Although tyrosine phosphorylation of extracellular proteins has been reported to occur extensively in vivo, no secreted protein tyrosine kinase has been identified. As a result, investigation of the potential role of extracellular tyrosine phosphorylation in physiological and pathological tissue regulation has not been possible. Here, we show that VLK, a putative protein kinase previously shown to be essential in embryonic development, is a secreted protein kinase, with preference for tyrosine, that phosphorylates a broad range of secreted and ER-resident substrate proteins. We find that VLK is rapidly and quantitatively secreted from platelets in response to stimuli and can tyrosine phosphorylate coreleased proteins utilizing endogenous as well as exogenous ATP sources. We propose that discovery of VLK activity provides an explanation for the extensive and conserved pattern of extracellular tyrosine phosphophorylation seen in vivo, and extends the importance of regulated tyrosine phosphorylation into the extracellular environment.

Hypoxia-inducible factor-mediated induction of WISP-2 contributes to attenuated progression of breast cancer

Hypoxia and the hypoxia-inducible factor (HIF) signaling pathway trigger the expression of several genes involved in cancer progression and resistance to therapy. Transcriptionally active HIF-1 and HIF-2 regulate overlapping sets of target genes, and only few HIF-2 specific target genes are known so far. Here we investigated oxygen-regulated expression of Wnt-1 induced signaling protein 2 (WISP-2), which has been reported to attenuate the progression of breast cancer. WISP-2 was hypoxically induced in low-invasive luminal-like breast cancer cell lines at both the messenger RNA and protein levels, mainly in a HIF-2α-dependent manner. HIF-2-driven regulation of the WISP2 promoter in breast cancer cells is almost entirely mediated by two phylogenetically and only partially conserved functional hypoxia response elements located in a microsatellite region upstream of the transcriptional start site. High WISP-2 tumor levels were associated with increased HIF-2α, decreased tumor macrophage density, and a better prognosis. Silencing WISP-2 increased anchorage-independent colony formation and recovery from scratches in confluent cell layers of normally low-invasive MCF-7 cancer cells. Interestingly, these changes in cancer cell aggressiveness could be phenocopied by HIF-2α silencing, suggesting that direct HIF-2-mediated transcriptional induction of WISP-2 gene expression might at least partially explain the association of high HIF-2α tumor levels with prolonged overall survival of patients with breast cancer.

Non-canonical HIF-2α function drives autonomous breast cancer cell growth via an AREG-EGFR/ErbB4 autocrine loop

Tumor progression is intrinsically tied to the clonal selection of tumor cells with acquired phenotypes allowing to cope with a hostile microenvironment. Hypoxia-inducible factors (HIFs) master the transcriptional response to local tissue hypoxia, a hallmark of solid tumors. Here, we report significantly longer patient survival in breast cancer with high levels of HIF-2α. Amphiregulin (AREG) and WNT1-inducible signaling pathway protein-2 (WISP2) expression was strongly HIF-2α-dependent and their promoters were particularly responsive to HIF-2α. The endogenous AREG promoter recruited HIF-2α in the absence of a classical HIF-DNA interaction motif, revealing a novel mechanism of gene regulation. Loss of AREG expression in HIF-2α-depleted cells was accompanied by reduced activation of epidermal growth factor (EGF) receptor family members. Apparently opposing results from patient and in vitro data point to an HIF-2α-dependent auto-stimulatory tumor phenotype that, while promoting EGF signaling in cellular models, increased the survival of diagnosed and treated human patients. Our findings suggest a model where HIF-2α-mediated autocrine growth signaling in breast cancer sustains a state of cellular self-sufficiency, thereby masking unfavorable microenvironmental growth conditions, limiting adverse selection and improving therapy efficacy. Importantly, HIF-2α/AREG/WISP2-expressing tumors were associated with luminal tumor differentiation, indicative of a better response to classical treatments. Shifting the HIF-1/2α balance toward an HIF-2-dominated phenotype could thus offer a novel approach in breast cancer therapy.

Onconeuronal cerebellar degeneration-related antigen, Cdr2, is strongly expressed in papillary renal cell carcinoma and leads to attenuated hypoxic response

The onconeuronal cerebellar degeneration-related antigen Cdr2 is associated with paraneoplastic syndromes. Neoplastic expression of Cdr2 in ovary and breast tumors triggers an autoimmune response that suppresses tumor growth by developing tumor immunity, but culminates in cerebellar degeneration when Cdr2-specific immune cells recognize neuronal Cdr2. We identified Cdr2 as a novel interactor of the hypoxia-inducible factor (HIF) prolyl-4-hydroxylase PHD1 and provide evidence that Cdr2 might represent a novel important tumor antigen in renal cancer. Strong Cdr2 protein expression was observed in 54.2% of papillary renal cell carcinoma (pRCC) compared with 7.8% of clear-cell RCC and no staining was observed in chromophobe RCC or oncocytoma. High Cdr2 protein levels correlated with attenuated HIF target gene expression in these solid tumors, and Cdr2 overexpression in tumor cell lines reduced HIF-dependent transcriptional regulation. This effect was because of both attenuation of hypoxic protein accumulation and suppression of the transactivation activity of HIF-1alpha. pRCC is known for its tendency to avascularity, usually associated with a lower pathological stage and higher survival rates. We provide evidence that Cdr2 protein strongly accumulates in pRCC, attenuates the HIF response to tumor hypoxia and may become of diagnostic importance as novel renal tumor marker.