Microtubule-associated protein 1S (MAP1S) bridges autophagic components with microtubules and mitochondria to affect autophagosomal biogenesis and degradation.

The ubiquitously distributed MAP1S is a homologue of the exclusively neuronal distributed microtubule-associated protein 1A and 1B (MAP1A/B). They give rise to multiple isoforms through similar post-translational modification. Isoforms of MAP1S have been implicated in microtubule dynamics and mitotic abnormalities and mitotic cell death. Here we show that ablation of the Map1s gene in mice caused reduction in the B-cell CLL/lymphoma 2 or xL (Bcl-2/xL) and cyclin-dependent kinase inhibitor 1B (P27) protein levels, accumulation of defective mitochondria, and severe defects in response to nutritive stress, suggesting defects in autophagosomal biogenesis and clearance. Furthermore, MAP1S isoforms interacted with the autophagosome-associated light chain 3 of MAP1A/B (LC3), a homologue of yeast autophagy-related gene 8 (ATG8), and recruited it to stable microtubules in a MAP1S and LC3 isoform-dependent mode. In addition, MAP1S interacted with mitochondrion-associated leucine-rich PPR-motif containing protein (LRPPRC) that interacts with the mitophagy initiator and Parkinson disease-related protein Parkin. The three-way interactions of MAP1S isoforms with LC3 and microtubules as well as the interaction of MAP1S with LRPPRC suggest that MAP1S isoforms may play positive roles in integration of autophagic components with microtubules and mitochondria in both autophagosomal biogenesis and degradation. For the first time, our results clarify roles of MAP1S in bridging microtubules and mitochondria with autophagic and mitophagic initiation, maturation, trafficking, and lysosomal clearance. Defects in the MAP1S-regulated autophagy may impact heart disease, cancers, neurodegenerative diseases, and a wide range of other diseases.

Fibroblast growth factor receptor 1 (FGFR1) tyrosine phosphorylation regulates binding of FGFR substrate 2alpha (FRS2alpha) but not FRS2 to the receptor.

Binding of the fibroblast growth factor (FGF) to the FGF receptor (FGFR) tyrosine kinase leads to receptor tyrosine autophosphorylation as well as phosphorylation of multiple downstream signaling molecules that are recruited to the receptor either by direct binding or through adaptor proteins. The FGFR substrate 2 (FRS2) family consists of two members, FRS2alpha and FRS2beta, and has been shown to recruit multiple signaling molecules, including Grb2 and Shp2, to FGFR1. To better understand how FRS2 interacted with FGFR1, in vivo binding assays with coexpressed FGFR1 and FRS2 recombinant proteins in mammalian cells were carried out. The results showed that the interaction of full-length FRS2alpha, but not FRS2beta, with FGFR1 was enhanced by activation of the receptor kinase. The truncated FRS2alpha mutant that was comprised only of the phosphotyrosine-binding domain (PTB) bound FGFR1 constitutively, suggesting that the C-terminal sequence downstream the PTB domain inhibited the PTB-FGFR1 binding. Inactivation of the FGFR1 kinase and substitutions of tyrosine phosphorylation sites of FGFR1, but not FRS2alpha, reduced binding of FGFR1 with FRS2alpha. The results suggest that although the tyrosine autophosphorylation sites of FGFR1 did not constitute the binding sites for FRS2alpha, phosphorylation of these residues was essential for optimal interaction with FRS2alpha. In addition, it was demonstrated that the Grb2-binding sites of FRS2alpha are essential for mediating signals of FGFR1 to activate the FiRE enhancer of the mouse syndecan 1 gene. The results, for the first time, demonstrate the specific signals mediated by the Grb2-binding sites and further our understanding of FGF signal transmission at the adaptor level.

Fibroblast growth factor receptor 2 tyrosine kinase is required for prostatic morphogenesis and the acquisition of strict androgen dependency for adult tissue homeostasis.

The fibroblast growth factor (FGF) family consists of 22 members and regulates a broad spectrum of biological activities by activating diverse isotypes of FGF receptor tyrosine kinases (FGFRs). Among the FGFs, FGF7 and FGF10 have been implicated in the regulation of prostate development and prostate tissue homeostasis by signaling through the FGFR2 isoform. Using conditional gene ablation with the Cre-LoxP system in mice, we demonstrate a tissue-specific requirement for FGFR2 in urogenital epithelial cells--the precursors of prostatic epithelial cells--for prostatic branching morphogenesis and prostatic growth. Most Fgfr2 conditional null (Fgfr2(cn)) embryos developed only two dorsal prostatic (dp) and two lateral prostatic (lp) lobes. This contrasts to wild-type prostate, which has two anterior prostatic (ap), two dp, two lp and two ventral prostatic (vp) lobes. Unlike wild-type prostates, which are composed of well developed epithelial ductal networks, the Fgfr2(cn) prostates, despite retaining a compartmented tissue structure, exhibited a primitive epithelial architecture. Moreover, although Fgfr2(cn) prostates continued to produce secretory proteins in an androgen-dependent manner, they responded poorly to androgen with respect to tissue homeostasis. The results demonstrate that FGFR2 is important for prostate organogenesis and for the prostate to develop into a strictly androgen-dependent organ with respect to tissue homeostasis but not to the secretory function, implying that androgens may regulate tissue homeostasis and tissue function differently. Therefore, Fgfr2(cn) prostates provide a useful animal model for scrutinizing molecular mechanisms by which androgens regulate prostate growth, homeostasis and function, and may yield clues as to how advanced-tumor prostate cells escape strict androgen regulations.

Chronic activity of ectopic type 1 fibroblast growth factor receptor tyrosine kinase in prostate epithelium results in hyperplasia accompanied by intraepithelial neoplasia.

BACKGROUND: Ectopic expression of fibroblast growth factor receptor 1 (FGFR1) tyrosine kinase in epithelial cells is associated with progression of prostate cancer. Ectopic expression by transfection of FGFR1 in premalignant epithelial cells from nonmalignant Dunning tumors accelerated time-dependent progression of epithelial cells to malignancy. This study was designed to test the effect of chronic androgen-dependent ectopic activity of FGFR1 in the normal adult mouse epithelium by gene targeting. MATERIALS AND METHODS: Constitutively active FGFR1 (caFGFR1) was targeted to prostate epithelial cells using the androgen-dependent probasin (PB) promoter. Prostate tissues of three strains were characterized over a period of 2 years by HE staining, immunohistochemical analyses for cytokeratin and alpha-actin, and rate of androgen-induced regeneration after castration. RESULTS: Relative to wildtype littermates, transgenic mice showed increased overall size, hyperplasia in epithelial, and, to a lesser extent, stromal compartments and nuclear atypia in epithelial cells of the prostate with increasing age. Androgen-induced regeneration after castration was enhanced at day 3 by two-fold in mice expressing ectopic caFGFR1. CONCLUSIONS: The ectopic presence and chronic activation of FGFR1 in mouse prostate epithelial cells induces progressive prostate intraepithelial neoplasia. These results confirm results suggested by the transplantable Dunning tumor and cell culture models that, in contrast to homeostasis-promoting resident FGFR2, chronic ectopic FGFR1 kinase activity in the epithelium disrupts homeostasis between stroma and epithelium. Although insufficient alone, it may cooperate with other oncogenic changes to promote epithelial cells down the path to malignancy.

Cooperation between ectopic FGFR1 and depression of FGFR2 in induction of prostatic intraepithelial neoplasia in the mouse prostate.

Disruption of the regulatory communication from the stroma to the epithelium mediated by the FGF7/10-FGFR2 signaling axis in the prostate and expression of ectopic FGFR1 in prostatic epithelial cells often correlate with prostate cancer progression both in human and in experimental animals. Ectopic expression of constitutively active FGFR1 mutant (caFGFR1) at low levels in prostate epithelial cells induces low- to intermediate-grade prostatic intraepithelial neoplasia (PIN) within 6-8 months and high-grade PIN in 20-25 months. Depression of the FGFR2 signaling in the prostate also disturbs homeostasis in the prostate and induces prostate hyperplasia. To study whether PIN lesions induced by the caFGFR1 were expression-level dependent, and whether expression of the caFGFR1 and depression of the FGFR2 signaling in the prostate synergistically disturbed prostate homeostasis, we generated two new strains of ARR2PBi-caFGFR1 transgenic mice, which highly expressed caFGFR1 in prostatic epithelial cells. The mice were crossed with KDNR mice to generate ARR2PBi-caFGFR1/KDNR bigenic mice. The ARR2PBi-caFGFR1 mice developed high-grade PIN within 8 months, which was significantly faster than the mice expressing caFGFR1 at low levels. In addition, depression of the FGFR2 signaling clearly promoted perturbation of cellular homeostasis induced by the caFGFR1. The results demonstrated that the PIN development in caFGFR1 transgenic mice was caFGFR1 dosage-dependent, and indicated that the ectopic FGFR1 and the resident FGFR2 in epithelial cells had opposite impacts on intercompartmental homeostasis in the prostate. The bigenic mice provide a model with cooperative aberrations in the fibroblast growth factor signaling axis for evaluation of tumor-initiating events in prostate tumorigenesis.

Transgenic mouse with high Cre recombinase activity in all prostate lobes, seminal vesicle, and ductus deferens.

BACKGROUND: Prostate-specific gene ablation provides a powerful tool for functional characterization of genes that have impact on embryonic development or on other organs, specifically in the prostate. Uniform expression of Cre with high recombinase activity in the prostate is needed for prostate-specific gene ablation based on Cre-loxP recombinations. Currently, available strains of Cre transgenic mice only express Cre recombinase adequately in certain lobes of the prostate. In other lobes, the expression is low and mosaic. Additional strains of transgenic mice expressing high levels of prostate-specific Cre in all prostate lobes would be useful to study the impact of genome manipulation in all prostate lobes. METHODS: The ARR2PB composite promoter with improved capacity to drive androgen-responsive gene expression was used to initiate expression of a transgene bearing the cDNA encoding a recently modified Cre recombinase with improved recombination activity. In addition, an insulator element from the chicken globin locus that minimized negative effect on transcription of the transgene imposed by chromosome structure was employed. The derived transgenic founders were crossed with the Z/AP reporter mouse and Fgfr2(f/f) mice bearing loxP flanking the FGFR2 locus. Immunochemical and mRNA analyses were employed to test expression and efficacy of the Cre recombinase in the prostate and other tissues. RESULTS: The ARR2PBi-Cre transgenic mouse specifically and uniformly expressed Cre recombinase in the dorsal, lateral, ventral, and anterior lobes of the prostate, seminal vesicles, and ductus deferens. The Cre recombinase in these tissues effectively excised loxP flanked DNA fragments in the Z/AP reporter that triggered expression of beta-galactosidase, and the loxP-flanked FGFR2(f/f) locus resulting in specific ablation of FGFR2 in the prostate. CONCLUSIONS: Compared with the currently available prostate-specific Cre strains, the new ARR2PBi-Cre strain exhibited higher and more uniform expression of Cre recombinase in the prostate as well as in seminal vesicles and ductus deferens. This provides an additional tool for efficient hormone-dependent gene targeting in epithelial cells of all lobes of the adult prostate, seminal vesicle, and ductus deferens.

Fibroblast growth factor receptor 1 phosphotyrosine 766: molecular target for prevention of progression of prostate tumors to malignancy.

Dissection of processes that promote the slow progression to malignancy from those that drive the malignant phenotype, once acquired, is important for identification of molecular targets for rational design of dietary and pharmaceutical intervention to hold premalignant cancer in check. In adult parenchymal organs, fibroblast growth factor receptor (FGFR) kinase isotypes are partitioned between stroma and epithelium, respectively, and mediate communication between the two compartments to maintain organ homeostasis. The ectopic appearance of stromal FGFR1 is a hallmark of epithelial cells from model transplantable rat prostate tumors that progress to malignancy. Here we show that, despite the fact that it is transcriptionally active, the appearance of FGFR1 in nonmalignant prostate tumor epithelial cells at first does not drive cell proliferation or support a malignant phenotype. These properties develop over time with proliferative aging of the cell population coincident with FGFR1-dependent activation of the mitogen-activated protein kinase signaling pathway. Phospholipase Cgamma-interactive phosphotyrosine 766 of FGFR1 is required for the age-dependent acquisition of the proliferative response to FGFR1, although it appears not to be required for the mitogenic response. Although of little utility in late-stage therapy, this suggests that pathways linked to FGFR1 tyrosine 766 may be specific targets for prevention of progression of latent nonmalignant tumors to the life-threatening malignant state.

The intracellular microenvironment in host cell-specific phosphorylation of SNT1 by the FGFR1 tyrosine kinase.

The phosphorylation of the fibroblast growth factor receptor (FGFR) kinase substrate SNT1 (also called FGFR substrate 2, FRS2) by FGFR tyrosine kinases is both host cell- and receptor isotype-specific. To study the determinants of the host cell-specific phosphorylation of SNT1 by FGFR1 tyrosine kinase, we constructed a chimeric receptor FGFR2IIIb/R1 that consisted of an FGFR2IIIb ligand-binding ectodomain and an FGFR1 tyrosine kinase domain. The chimeric FGFR2IIIb/R1 kinase mediated robust phosphorylation of SNT1 immediately after transfection in mouse 3T3 cells where the FGFR1 kinase was residential, and in proliferative aged prostate tumor epithelial cells (DTE-R1/100) that ectopically expressed FGFR1 kinase. This is in contrast to the fact that the robust phosphorylation of SNT1 by ectopic FGFR1 kinase is an acquisition property in DTE premalignant prostate epithelial cells, which normally do not express FGFR1. The data suggest that the microenvironment of intracellular, rather than components in the extracellular compartment, of host cells is important in permitting FGFR1 kinase to strongly phosphorylate SNT1. Together with our previous data that the acquisition of SNT1 phosphorylation activity is concurrent with the acquisition of mitogenic activity of FGFR1 in prostate epithelial cells, the results here further demonstrate that the phosphorylation of SNT1 is host cell specific and that alterations induced by chronic exposure to ectopic FGFR1 kinase are involved in acquisition of SNT1 phosphorylation activity to the ectopic FGFR1 in prostate epithelial cells.