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Biomedical subjects

Larry S Sherman

Publications and source records attributed to Larry S Sherman.

15 recordsLinked to original sources
PubMed2005

Brg1 is required for murine neural stem cell maintenance and gliogenesis.

Epigenetic alterations in cell-type-specific gene expression control the transition of neural stem cells (NSCs) from predominantly neurogenic to predominantly gliogenic phases of differentiation, but how this switch occurs is unclear. Here, we show that brahma-related gene 1 (Brg1), an ATP-dependent chromatin remodeling factor, is required for the repression of neuronal commitment and the maintenance of NSCs in a state that permits them to respond to gliogenic signals. Loss of Brg1 in NSCs in conditional brg1 mutant mice results in precocious neuronal differentiation, such that cells in the ventricular zone differentiate into post-mitotic neurons before the onset of gliogenesis. As a result, there is a dramatic failure of astrocyte and oligodendrocyte differentiation in these animals. The ablation of brg1 in gliogenic progenitors in vitro also prevents growth-factor-induced astrocyte differentiation. Furthermore, proteins implicated in the maintenance of stem cells, including Sox1, Pax6 and Musashi-1, are dramatically reduced in the ventricular zones of brg1 mutant mice. We conclude that Brg1 is required to repress neuronal differentiation in NSCs as a means of permitting glial cell differentiation in response to gliogenic signals, suggesting that Brg1 regulates the switch from neurogenesis to gliogenesis.

Animals↗
PubMed2005

Protein 4.1B expression is induced in mammary epithelial cells during pregnancy and regulates their proliferation.

4.1B is a member of the protein 4.1 superfamily of proteins that link transmembrane proteins to the actin cytoskeleton. The 4.1B gene localizes to chromosome 18p11.3, which undergoes loss of heterozygosity in mammary tumors. Here, we examine the expression of 4.1B in murine mammary epithelium and find that 4.1B is dramatically upregulated in mammary epithelial cells during pregnancy when there is extensive cell proliferation. In contrast, 4.1B is not expressed in virgin, lactating, or involuting mammary epithelium. To examine the consequence of 4.1B loss on mammary epithelial cell proliferation, we analysed mammary glands in 4.1B-null mice. 4.1B loss results in a significant increase in mammary epithelial cell proliferation during pregnancy, but has no effect on mammary epithelial cell proliferation, in virgin or involuting mice. Furthermore, we show that 4.1B inhibits the proliferation of mammary epithelial cell lines by inducing a G1 cell cycle arrest, characterized by decreased cyclin A expression and reduced Rb phosphorylation, and accompanied by reduced erbB2 phosphorylation. This cell cycle arrest does not involve alterations in the activities of MAPK, JNK, or Akt. Collectively, our findings demonstrate that 4.1B regulates mammary epithelial cell proliferation during pregnancy and suggest that its loss may influence mammary carcinoma pathogenesis in multiparous women.

Animals↗
PubMed2005

Hyaluronan accumulates in demyelinated lesions and inhibits oligodendrocyte progenitor maturation.

Demyelination is the hallmark of numerous neurodegenerative conditions, including multiple sclerosis. Oligodendrocyte progenitors (OPCs), which normally mature into myelin-forming oligodendrocytes, are typically present around demyelinated lesions but do not remyelinate affected axons. Here, we find that the glycosaminoglycan hyaluronan accumulates in demyelinated lesions from individuals with multiple sclerosis and in mice with experimental autoimmune encephalomyelitis. A high molecular weight (HMW) form of hyaluronan synthesized by astrocytes accumulates in chronic demyelinated lesions. This form of hyaluronan inhibits remyelination after lysolecithin-induced white matter demyelination. OPCs accrue and do not mature into myelin-forming cells in demyelinating lesions where HMW hyaluronan is present. Furthermore, the addition of HMW hyaluronan to OPC cultures reversibly inhibits progenitor-cell maturation, whereas degrading hyaluronan in astrocyte-OPC cocultures promotes oligodendrocyte maturation. HMW hyaluronan may therefore contribute substantially to remyelination failure by preventing the maturation of OPCs that are recruited to demyelinating lesions.

Animals↗
PubMed2005

SWI/SNF chromatin-remodeling factors induce changes in DNA methylation to promote transcriptional activation.

Brahma (Brm) and brahma-related gene-1 (Brg1) are mammalian homologues of SWI/SNF chromatin-remodeling factor subunits that can regulate both transcriptional activation and repression. Both Brg1 and Brm are mutated or deleted in numerous cancer cell lines, leading to the altered expression of genes that influence cell proliferation and metastasis. Here, we find that the promoters of two such genes, CD44 and E-cadherin, are hypermethylated in cells that have lost Brg1 or Brm. In two carcinoma cell lines that lack functional Brg1 and Brm, CD44 and E-cadherin expression are induced by the demethylating agent 5-aza-2'-deoxycytidine. Transfection with either Brg1 or Brm also induces CD44 and E-cadherin transcription and protein expression in these cells, as well as loss of methylation at sequences in the promoters of both genes. Chromatin immunoprecipitation assays show that Brg1 and Brm associate with these regions of the CD44 and E-cadherin promoters, suggesting that SWI/SNF protein complexes may directly influence the loss of DNA methylation. In vivo, Brm-deficient mice also show methylation and silencing of the CD44 promoter. Collectively, these data implicate loss of SWI/SNF-mediated transcriptional activation as a novel mechanism to increase DNA methylation in cancer cells and provide insight into the mechanisms underlying aberrant gene induction and repression during tumor progression.

Adenocarcinoma↗
PubMed2005

Coordinate control of axon defasciculation and myelination by laminin-2 and -8.

Schwann cells form basal laminae (BLs) containing laminin-2 (Ln-2; heterotrimer alpha2beta1gamma1) and Ln-8 (alpha4beta1gamma1). Loss of Ln-2 in humans and mice carrying alpha2-chain mutations prevents developing Schwann cells from fully defasciculating axons, resulting in partial amyelination. The principal pathogenic mechanism is thought to derive from structural defects in Schwann cell BLs, which Ln-2 scaffolds. However, we found loss of Ln-8 caused partial amyelination in mice without affecting BL structure or Ln-2 levels. Combined Ln-2/Ln-8 deficiency caused nearly complete amyelination, revealing Ln-2 and -8 together have a dominant role in defasciculation, and that Ln-8 promotes myelination without BLs. Transgenic Ln-10 (alpha5beta1gamma1) expression also promoted myelination without BL formation. Rather than BL structure, we found Ln-2 and -8 were specifically required for the increased perinatal Schwann cell proliferation that attends myelination. Purified Ln-2 and -8 directly enhanced in vitro Schwann cell proliferation in collaboration with autocrine factors, suggesting Lns control the onset of myelination by modulating responses to mitogens in vivo.

Animals↗
PubMed2005

Erbin regulates mitogen-activated protein (MAP) kinase activation and MAP kinase-dependent interactions between Merlin and adherens junction protein complexes in Schwann cells.

Biallelic mutations in the neurofibromatosis 2 (NF2) gene are linked to schwannoma and meningioma tumorigenesis. Cells with NF2 mutations exhibit elevated levels of phosphorylated extracellular signal-regulated kinase (ERK) and aberrant cell-cell and cell-matrix contacts. The NF2 gene product, merlin, associates with adherens junction protein complexes, suggesting that part of its function as a tumor suppressor involves regulating cell junctions. Here, we find that a novel PDZ protein, called erbin, binds directly to the merlin-binding partner, EBP0, and regulates adherens junction dissociation through a MAP kinase-dependent mechanism. Reducing erbin expression using a targeted siRNA in primary cultures of Schwann cells results in altered cell-cell interactions, disruption of E-cadherin adherens junctions, increased cell proliferation, and elevated levels of phosphorylated ERK, all phenotypes observed in cells that lack merlin. Reduction of erbin expression also results in the dissociation of merlin from adherens junction proteins and an increase in the levels of phosphorylated merlin. These phenotypes can be rescued if cells with reduced levels of erbin are treated with a pharmacological inhibitor of ERK kinase. Collectively, these data indicate that erbin regulates MAP kinase activation in Schwann cells and suggest that erbin links merlin to both adherens junction protein complexes and the MAP kinase signaling pathway.

Adherens Junctions↗
PubMed2005

Disruption of the hyaluronan-based extracellular matrix in spinal cord promotes astrocyte proliferation.

Astrocyte proliferation is tightly controlled during development and in the adult nervous system. In the present study, we find that a high-molecular-weight (MW) form of the glycosaminoglycan hyaluronan (HA) is found in rat spinal cord tissue and becomes degraded soon after traumatic spinal cord injury. Newly synthesized HA accumulates in injured spinal cord as gliosis proceeds, such that high-MW HA becomes overabundant in the extracellular matrix surrounding glial scars after 1 month. Injection of hyaluronidase, which degrades HA, into normal spinal cord tissue results in increased numbers of glial fibrillary acidic protein (GFAP)-positive cells that also express the nuclear proliferation marker Ki-67, suggesting that HA degradation promotes astrocyte proliferation. In agreement with this observation, adding high- but not low-MW HA to proliferating astrocytes in vitro inhibits cell growth, while treating confluent, quiescent astrocyte cultures with hyaluronidase induces astrocyte proliferation. Collectively, these data indicate that high-MW HA maintains astrocytes in a state of quiescence, and that degradation of HA following CNS injury relieves growth inhibition, resulting in increased astrocyte proliferation.

Animals↗
PubMed2004

CD44 expression identifies astrocyte-restricted precursor cells.

The precise lineage between neural stem cells and mature astrocytes remains poorly defined. To examine astrocyte development, we have characterized glial precursors from neural tissue derived from early embryonic ages. We show that CD44 identifies an astrocyte-restricted precursor cell (ARP) that is committed to generating astrocytes in vitro and in vivo in both rodent and human tissue. CD44+ cells arise later in development than neuronal-restricted precursors (NRPs) or tripotential glial-restricted precursors (GRPs). ARPs are distinguished from GRP and NRP cells by their antigenic profile and differentiation ability. ARPs can be generated from GRP cells in mass or clonal cultures and in vivo after transplantation, suggesting a sequential differentiation of neuroepithelial stem cells (NEPs) to GRPs to ARPs and then to astrocytes. The properties of ARPs are different from other astrocyte precursors described previously in their expression of CD44 and S-100beta and absence of other lineage markers. Using a CD44 misexpression transgenic mouse model (CNP-CD44 mouse), we show that CD44 overexpression in vivo and in vitro decreases the number of mature glia and increases the number of O4+/GFAP+ cells tenfold. Misexpression of CD44 in culture inhibits oligodendrocytes and arrests cells at the precursor state. In summary, our data provide strong evidence for the existence of a CD44+ ARP in the developing nervous system.

Animals↗
PubMed2004

CD44-independent hepatocyte growth factor/c-Met autocrine loop promotes malignant peripheral nerve sheath tumor cell invasion in vitro.

Malignant peripheral nerve sheath tumors (MPNSTs) are invasive peripheral nerve neoplasms that express both the receptor tyrosine kinase c-Met and its ligand hepatocyte growth factor (HGF). The combined expression of these proteins has been implicated in tumor cell growth and metastasis. However, HGF/c-Met autocrine activity requires the presence of a serine protease, the HGF activator (HGFA), and, in some cells, the CD44 transmembrane glycoprotein. Here, we found that HGFA, HGF, c-Met, and CD44 are coexpressed in MPNSTs but their localization did not correlate with increased cell proliferation. The ST8814 MPNST cell line also expresses all of these proteins, can convert pro-HGF to active HGF, and exhibits constitutive c-Met phosphorylation. Blocking c-Met activity or expression inhibits the invasive behavior of these cells but not their proliferation. Interestingly, although a CD44 splice variant contributes to MPNST cell invasion and interacts with c-Met and HGF in ST8814 cells, it is not required for c-Met activation. These data indicate that an HGF/c-Met autocrine loop can promote MPNST invasion through a CD44-independent mechanism and suggest that c-Met, HGFA, and HGF are potential molecular targets to inhibit MPNST metastasis.

Autocrine Communication↗
PubMed2004

CD44 overexpression by oligodendrocytes: a novel mouse model of inflammation-independent demyelination and dysmyelination.

The CD44 transmembrane glycoprotein family has been implicated in cell-cell adhesion and cell signaling in response to components of the extracellular matrix but its role in the nervous system is not understood. CD44 proteins are elevated in Schwann cells and oligodendrocytes following nervous system insults, in inflammatory demyelinating lesions, and in tumors. Here, we tested the hypothesis that elevated CD44 expression influences Schwann cell and oligodendrocyte functions by generating transgenic mice that express CD44 under the control of the 2',3'-cyclic nucleotide-3'-phosphodiesterase (CNPase) promoter. These mice failed to develop peripheral nerve or CNS tumors. However, they did develop severe tremors that were associated with CNS dysmyelination and progressive demyelination. Loss of CNS myelin was not due to alterations in early oligodendrocyte precursor differentiation, proliferation, or survival. Myelination in the PNS appeared normal. In no instance was there any evidence of an inflammatory response that could account for the loss of CNS myelin. These findings suggest that CNPase-CD44 mice are a novel model for noninflammatory progressive demyelinating disease and support a potential role for CD44 proteins expressed by glial cells in promoting demyelination.

Animals↗
PubMed2003

Malignant peripheral nerve sheath tumor cell invasion is facilitated by Src and aberrant CD44 expression.

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive malignancies that arise within peripheral nerves. These tumors occur with increased incidence in patients with neurofibromatosis type 1 (NF1), exhibiting increased Ras activity due to loss of the NF1 gene product, neurofibromin, and abnormal expression of the epidermal growth factor receptor (EGFR). We previously found that MPNSTs express increased levels of the CD44 family of transmembrane glycoproteins that have been implicated in tumor cell invasion and metastasis. In two MPNST cell lines, we have found that elevated CD44 expression and cell invasion are dependent on Src kinase activity but are independent of mitogen-activated protein kinases (MAPK) kinase (MEK) activity. In contrast, inhibition of Src kinase activity has no influence on MPNST cell proliferation. Reduction of CD44 levels, using antisense oligonucleotides, results in reduced MPNST cell invasion in vitro, suggesting that Src contributes in part to MPNST cell invasion by increasing CD44 levels. At least some of this increased CD44 expression results from elevated EGFR levels through a Src-dependent mechanism, consistent with the notion that EGFR promotes constitutive Src activation in MPNSTs. These data indicate that Src and CD44 are putative targets for the treatment of MPNST invasion and metastasis.

Enzyme Inhibitors↗
PubMed2002

Concomitant down-regulation of BRM and BRG1 in human tumor cell lines: differential effects on RB-mediated growth arrest vs CD44 expression.

Mammalian cells express two homologs of the SWI2 subunit of the SWI/SNF chromatin-remodeling complex called BRG1 and BRM. Whether the SWI/SNF complexes formed by these two subunits perform identical or different functions remains an important question. In this report, we show concomitant down-regulation of BRG1 and BRM in six human tumor cell lines. This down-regulation occurs at the level of mRNA abundance. We tested whether BRM could affect aberrant cellular functions attributed to BRG1 in tumor cell lines. By transient transfection, we found that BRM can restore RB-mediated cell cycle arrest, induce expression of CD44 protein and suppress Cyclin A expression. Therefore, BRM may be consistently down-regulated with BRG1 during neoplastic progression because they share some redundant functions. However, assorted tissues from BRM null/BRG1-positive mice lack CD44 expression, suggesting that BRM-containing SWI/SNF complexes regulate expression of this gene under physiological conditions. Our studies further define the mechanism by which chromatin-remodeling complexes participate in RB-mediated cell cycle arrest and provide additional novel evidence that the functions of SWI/SNF complexes containing BRG1 or BRM are not completely interchangeable.

Animals↗
PubMed2002

CD44 associates with EGFR and erbB2 in metastasizing mammary carcinoma cells.

Type I receptor tyrosine kinases, including the epidermal growth factor receptor (EGFR) and erbB2, have been implicated in mammary carcinoma growth and metastasis. Recent evidence suggests that type I receptor signaling may be mediated by the CD44 family of transmembrane glycoproteins that also have been implicated in mammary tumor progression. Here, the authors tested whether CD44, EGFR, and erbB2 interacted and colocalized with one another in four mammary carcinoma cell lines (MCF-7, MDA-MB-231, MDA-MB-435, and MDA-MB-436) and in cytology samples obtained from patients with metastatic breast cancer. CD44 constitutively colocalized and coimmunoprecipitated with erbB2 and EGFR in all four mammary carcinoma cell lines. CD44 also colocalized with erbB2 and EGFR in all cytology samples expressing erbB2. CD44 colocalized with EGFR in cells from only 1 of 16 erbB2-negative cytology samples. These data indicate that CD44-EGFR-erbB2 protein complexes occur in a high proportion of metastatic mammary carcinomas and suggest that CD44-type I receptor colocalization may be a novel prognostic marker for aggressive mammary cancers.

Blotting, Western↗
PubMed2002

Endometrial carcinoma cells are nonpermissive for CD44-erbB2 interactions.

The erbB2 receptor tyrosine kinase and the CD44 transmembrane glycoprotein interact with one another in numerous cell types. This interaction helps to maintain erbB2 activity that contributes to tumor progression. We investigated whether CD44 and erbB2 similarly interact in endometrial carcinomas in vitro and in situ. In contrast to other carcinomas, CD44 did not colocalize with erbB2 in any of the 51 cases of endometrial cancer analyzed. CD44 also did not coimmunoprecipitate or colocalize with erbB2 in two endometrial carcinoma cell lines. We propose that the lack of CD44-erbB2 interactions may reduce the contribution of erbB2 to endometrial carcinoma progression.

Endometrial Neoplasms↗