Biomedical subjects

S T Dougherty

Publications and source records attributed to S T Dougherty.

8 recordsLinked to original sources

PubMed1999

Alternatively spliced CD44 isoforms containing exon v10 promote cellular adhesion through the recognition of chondroitin sulfate-modified CD44.

Correlations have been noted between the expression of certain alternatively spliced CD44 isoforms and the metastatic propensity of various histologically distinct tumor cell types. The precise mechanism by which particular CD44 isoforms contribute to the metastatic process is, however, unclear. In the present study we demonstrate that CD44R2, a CD44 isoform highly expressed on activated and transformed hemopoietic cells, can recognize and bind a common determinant present on CD44H and CD44R1. Importantly, CD44H lacked this activity. Pretreatment of TIL1 cells expressing CD44H or CD44R1 with chondroitinase ABC inhibited adhesion to CD44R2, suggesting that the unique inserted region present within the CD44R2 molecule, encoded by exon v10, mediates cell adhesion by potentiating the recognition of chondroitin sulfate moieties presented in association with other CD44 molecules. These data help explain the differential involvement of v10-containing CD44 isoforms in tumor metastasis.

Adjuvants, Immunologic↗

PubMed1999

Identification and characterization of CD44RC, a novel alternatively spliced soluble CD44 isoform that can potentiate the hyaluronan binding activity of cell surface CD44.

Soluble CD44 proteins generated by proteolytic cleavage or aberrant intron retention have been shown to antagonize the ligand binding activity of the corresponding cell surface receptor, inducing apoptosis and inhibiting tumor growth. Interestingly, such findings appear to contradict recent studies demonstrating a correlation between the presence of high levels of soluble CD44 in the serum of cancer patients and poor prognosis. In the present study, we report the cloning of a novel, naturally occurring, differentially expressed, soluble CD44 isoform, designated CD44RC, which, in contrast to previously described soluble CD44 proteins, can dramatically enhance the hyaluronan binding activity of cell surface CD44. Sequence analysis suggests that CD44RC is generated by an alternative splicing event in which the 3' end of CD44 exon 2 is spliced into an internal splice acceptor site present within exon 18, altering reading frame and giving rise to a soluble protein with a unique COOH terminus. Functional studies suggest that CD44RC enhances hyaluronan binding by adhering to chondroitin sulfate side-chains attached to cell surface CD44, generating a multivalent complex with increased avidity for hyaluronan.

Adjuvants, Immunologic↗

PubMed1997

Molecular mechanisms regulating TNF-alpha production by tumor-associated macrophages.

The molecular mechanisms that regulate the production and/or functional activity of intratumoral tumor necrosis factor-alpha (TNF-alpha) remain poorly defined. To begin to address this issue we have examined the level of TNF-alpha mRNA and protein produced by macrophages present within immunogenic Fsa-R and non-immunogenic Fsa-N tumors grown in syngeneic Lps(d) C3H/HeJ and Lps(n) C3H/HeN mice. The results obtained indicate that macrophages isolated from tumors grown in Lps(d) C3H/HeJ mice express 5-10-fold less TNF-alpha than equivalent cells present in tumors grown in Lps(n) C3H/HeN mice. These data suggest that the mechanisms that operate within the tumor microenvironment to induce the production of TNF-alpha act, at least in part, via the same signal transduction pathway that is defective in Lps(d) C3H/HeJ mice. Interestingly, despite such differences in TNF-alpha production, tumors inoculated into C3H/HeJ and C3H/HeN mice grew at a similar rate and contained an almost identical proportion of macrophages. Moreover, tumor cells purified from tumors grown in C3H/HeJ and C3H/HeN mice produced similar quantities of the TNF-alpha-inducible cytokine GM-CSF. Thus, although differences in the level of TNF-alpha produced within tumors grown in C3H/HeN and C3H/HeJ mice are readily demonstrable, such differences appear to have little direct impact on the outcome of tumor growth.

Animals↗

PubMed1997

Role of macrophage-colony-stimulating factor in regulating the accumulation and phenotype of tumor-associated macrophages.

In order to better define the role played by tumor-cell-derived macrophage-colony-stimulating factor (M-CSF) in regulating the recruitment and phenotype of tumor-associated macrophages, Polyoma large T-transformed fibroblastoid cell lines, derived from M-CSF-deficient osteopetrotic op/op mice and their phenotypically normal op/+ littermate controls, were inoculated into SCID (severe combined immunodeficiency) recipients and both the proportion and phenotype of the macrophages present within the tumors generated were determined. The results obtained indicate that, although tumors derived from M-CSF-deficient and M-CSF-producing tumor cell inoculate contain a similar proportion of macrophages, the macrophages isolated from tumors lacking M-CSF appear morphologically less mature and express lower levels of interleukin 1 beta, tumor necrosis factor alpha and FcR gamma II mRNA. Taken together, these data suggest that, although M-CSF does not appear to play a critical role in determining the macrophage content of these tumors, it does play a role in modulating the phenotype, and potentially the functional activity of the macrophages present within the tumor microenvironment.

Animals↗

PubMed1995

Adhesive interactions between alternatively spliced CD44 isoforms.

Alternative splicing of a series of 10 contiguous exons present within the CD44 gene can generate a large number of differentially expressed CD44 isoforms that contain additional peptide sequences of varying length inserted into a single site within the extracellular domain of the molecule proximal to the membrane spanning domain. Although distinct functions have been ascribed to certain of these isoforms, the effect of particular inserted domains on the ligand-binding specificity of the CD44 molecule remains unclear. In the present study, we demonstrate that while CD44H, the major CD44 isoform expressed on resting hemopoietic cells, and CD44R1, an alternatively spliced isoform present on transformed epithelial cells and certain activated and/or malignant hemopoietic cell types, can both bind avidly to hyaluronan, only CD44R1 can promote homotypic cellular aggregation when expressed in the CD44-negative murine lymphoma cell line TIL1. Experiments in which TIL1 cells transduced with different CD44 isoforms were tested for their ability to adhere to one another or to COS7 cells transfected with CD44R1, indicated that CD44R1 can recognize and bind a common determinant present on both CD44H and CD44R1. Monoclonal antibody blocking studies suggest further, that the determinant recognized by CD44R1 is located in a region of the CD44 molecule distinct from that involved in hyaluronan binding.

Alternative Splicing↗

PubMed1995

Molecular mechanisms regulating the hyaluronan binding activity of the adhesion protein CD44.

In the present study, we describe the isolation and characterization of a cDNA clone designated B6F1.3, that appears to 'activate' the hyaluronan-binding capacity of CD44 upon transfection into the murine fibroblastoid cell line MOP8. Sequence analysis indicates that the putative regulatory molecule encoded by this clone is identical to the murine interleukin-2 receptor gamma chain (mIL-2R gamma), a recently described type 1 transmembrane protein that constitutes an integral component of the cell surface receptors that bind a number of cytokines including IL-2, IL-4, IL-7, IL-9, IL-15 and perhaps also IL-13. Mutations in this molecule have been shown to be responsible for X-linked severe combined immunodeficiency (XSCID) in humans. With the exception of bone marrow, the mIL-2R gamma chain was found to be expressed at high levels on all hemopoietic cell lines and tissue types examined. Non-hemopoietic tissues are generally negative. FACS analysis and Western blot analysis indicated respectively that B6F1.3 does not mediate its effects by upregulating the expression of CD44 or by altering the alternative splicing of the molecule. Removal of the cytoplasmic tail of the mIL-2R gamma chain, including a Src homology region 2 (SH2) subdomain, abolished its ability to enhance CD44-mediated binding to hyaluronan suggesting the involvement of signal transduction events triggered via the cytoplasmic domain in the 'activation' process. Determining whether activating molecules such as B6F1.3 are co-expressed within tumor cells may help improve the potential value of CD44 as a diagnostic marker of metastatic disease.

Alternative Splicing↗

PubMed1995

Modification of tumor microenvironment by cytokine gene transfer.

The tumor microenvironment is determined by the interactions between host and tumor cells, a process in which cytokines play a major role. We have used retroviral vectors to insert and express cytokine genes in tumor cells so as to induce predictable changes in the host cells that infiltrate tumors. This frequently caused changes in tumor cell phenotype through autocrine/intracrine pathways. We reasoned that cytokine-induced alterations in tumor cell phenotype and/or in infiltrating host cells might alter the in vitro and in vivo cellular response to irradiation. In the present paper we document some of the effects of expression of interleukin-6 (IL-6) and IL-7 genes in tumor cells in this regard. The studies support the hypothesis that cytokines may play a role in determining both intrinsic tumor radioresponsiveness and the tumor microenvironment and in these ways may influence in vivo tumor irradiation responses. Possible cytokine gene-mediated approaches to radiotherapy cancer are discussed.

Animals↗

PubMed1989

Identification and characterization of 114/A10, an antigen highly expressed on the surface of murine myeloid and erythroid progenitor cells and IL-3-dependent cell lines.

Monoclonal antibody (mAb) 114/A10, raised against the murine bone marrow-derived multipotential hemopoietic progenitor cell line B6SUtA, identifies an antigen highly expressed by various interleukin-3 (IL-3)-dependent cell lines, the myelomonocytic cell line WEHI-3, and a large proportion of primary myeloid and erythroid colony-forming cells. Spleen- and bone marrow-derived 114/A10-positive cells were shown to selectively proliferate in vitro in response to pokeweed mitogen-stimulated spleen cell-conditioned medium or recombinant IL-3. Western blot analysis indicated that the antigen recognized by mAb 114/A10 has a mean relative molecular mass of approximately 150,000, although it is extremely heterogeneous in nature, and differs greatly in size range among different cell lines.

Animals↗