Restricted epithelial proliferation by lacritin via PKCalpha-dependent NFAT and mTOR pathways

Deoxycorticosterone Acetate-Salt Mice Exhibit Blood Pressure–Independent Sexual Dimorphism

We tested the hypothesis that female and male mice differ in terms of cardiac hypertrophy after deoxycorticosterone acetate (DOCA)+salt hypertension (uninephrectomy and 1% saline in drinking water) and focused on calcineurin signaling. We excluded confounding effects of blood pressure elevation or sex-related blood pressure differences by treating DOCA-salt mice with hydralazine (250 mg/L in drinking water). We found that directly measured mean arterial blood pressure was lowered to control values with hydralazine and corroborated this finding in separate mouse groups with radiotelemetry. Male mice were more responsive to DOCA-salt–related effects. They developed more left ventricular hypertrophy and more renal hypertrophy after 6 weeks of DOCA-salt+hydralazine compared with female mice. In hearts, transcripts for calcineurin Aβ and for myocyte-enriched calcineurin interacting protein 1 were upregulated in male but not in female mice. Enhanced activity of calcineurin Aβ, as indicated by diminished phosphorylation of NFATc2 in male mice, accounted for this sex-specific difference. Stretch-related, inflammatory, and profibrotic responses were also accentuated in male mice, as shown by higher transcript levels of atrial natriuretic peptide, monocyte chemoattractant protein-1, and transforming growth factor-β. Our results support sex-specific regulation of the calcineurin pathway in response to largely blood pressure–independent mineralocorticoid action. We suggest that sex-specific calcineurin activation determines the maladaptive cardiac and renal hypertrophic responses and accompanying organ injury in male mice.

Role of sarco/endoplasmic reticulum calcium content and calcium ATPase activity in the control of cell growth and proliferation

Ca(2+), the main second messenger, is central to the regulation of cellular growth. There is increasing evidence that cellular growth and proliferation are supported by a continuous store-operated Ca(2+) influx. By controlling store refilling, the sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA) also controls store-operated calcium entry and, thus, cell growth. In this review, we discuss data showing the involvement of SERCA in the regulation of proliferation and hypertrophy. First, we describe the Ca(2+)-related signaling pathways involved in cell growth. Then, we present evidence that SERCA controls proliferation of differentiated cells and hypertrophic growth of cardiomyocytes, and discuss the role of SERCA isoforms. Last, we consider the potential therapeutic applications of increasing SERCA activity for the treatment of cardiovascular diseases and of modulating SERCA and SR content for the treatment of cancer.

Establishment of an appropriate animal model for lacritin studies: cloning and characterization of lacritin in monkey eyes

Lacritin is a mitogen of human salivary gland cells as well as a stimulator of human corneal epithelial cells. It is expected to be an important factor in maintaining the surrounding ocular surface. The monkey would be a relevant animal model in which to study the role of lacritin in ophthalmic physiology and pathology. However, to our knowledge, no cDNA cloning or functional analysis of monkey lacritin has been performed. Thus, the purposes of this study were: (1) to clone the monkey ortholog of lacritin; (2) to characterize lacritin in tears from several species; and (3) to determine the tissues where lacritin is produced and secreted. cDNA for lacritin from rhesus macaque contained 547 bp, with 411 bp in an open reading frame (ORF) encoding a protein of 137 amino acids. Monkey lacritin showed 89% amino acid homology with human lacritin; one amino acid was deleted in all three monkey strains. The predicted MW of mature lacritin was 12.2 kDa, and the isoelectric point was 4.99. Lacritin showed anomalous migration at approximately 21.0 kDa on SDS-PAGE, as confirmed by immunoblotting and amino acid sequencing. Similar to native lacritin in monkey tears, a 21 kDa band was also detected in human tears. In contrast, no lacritin was observed at a similar position on SDS-PAGE in rat, rabbit and dog tears. In the monkey, lacritin mRNA was expressed highly in the lacrimal gland, moderately in the conjunctiva and the meibomian gland, and weakly in corneal epithelium. In primates, lacritin was produced in the lacrimal gland and secreted into tear fluid. These results suggest that lacritin might be important for the maintenance of the ocular surface in higher animals, such as monkeys and humans.

Heparanase deglycanation of syndecan-1 is required for binding of the epithelial-restricted prosecretory mitogen lacritin

Cell surface heparan sulfate (HS) proteoglycans are carbohydrate-rich regulators of cell migratory, mitogenic, secretory, and inflammatory activity that bind and present soluble heparin-binding growth factors (e.g., fibroblast growth factor, Wnt, Hh, transforming growth factor β, amphiregulin, and hepatocyte growth factor) to their respective signaling receptors. We demonstrate that the deglycanated core protein of syndecan-1 (SDC1) and not HS chains nor SDC2 or -4, appears to target the epithelial selective prosecretory mitogen lacritin. An important and novel step in this mechanism is that binding necessitates prior partial or complete removal of HS chains by endogenous heparanase. This limits lacritin activity to sites where heparanase appears to predominate, such as sites of exocrine cell migration, secretion, renewal, and inflammation. Binding is mutually specified by lacritin's C-terminal mitogenic domain and SDC1's N terminus. Heparanase modification of the latter transforms a widely expressed HS proteoglycan into a highly selective surface-binding protein. This novel example of cell specification through extracellular modification of an HS proteoglycan has broad implications in development, homeostasis, and disease.