Expression of c-sis and other cellular proto-oncogenes in human sarcoma cell lines and biopsies

Absence of Expression of c-sis and Transforming Growth Factor-β mRNA in Malignant Fibrous Histiocytoma

Total RNA was extracted from five malignant fibrous histiocytomas and two benign fibrohistiocytic lesions and assayed for mRNA expressions for transforming growth factor beta (TGF-β) and c-sis by Northern blot analysis. Production of both of these has been associated with cells of monocyte-macrophage lineage, and these factors have been shown to be important in physiologic mesenchymal cell proliferation. No mRNA expression of either TGF-β or c-sis was identified in any of the fibrohistiocytic tumor samples. The lack of expression of TGF-β and c-sis may be consistent with a nonhistiocytic origin of malignant fibrous histiocytoma, or may reflect transformation- associated loss of the normal molecular mechanisms of mesenchymal proliferation. The absence of c-sis mRNA expression can be reconciled with the prior immunohisto chemical demonstration of platelet-derived growth factor in tumor cells of malignant fibrous histiocytoma. Int J Surg Pathol(2):117-122, 1993

Molecular targets in therapy for human soft-tissue and bone sarcomas

Sarcomas represent a heterogeneous group of tumors with different natural histories and therapeutic approaches. Recent discoveries have identified molecular alterations in the pathogenesis of these tumors that lead to distinct effects on sarcoma cell biology. These tumor cell characteristics include independence from growth factors, evasion of apoptosis, and maintenance of genomic integrity. Inhibition of these molecular alterations represents a therapeutic opportunity to reverse the biologic basis of tumor formation in soft-tissue sarcomas and bone tumors.

Alpha5 and alpha2 integrin gene transfers mimic the PDGF-B-induced transformed phenotype of fibroblasts in human skin

Platelet-derived growth factor (PDGF)-B is a proto-oncogene capable of transforming fibroblasts. Using adenoviral vectors, we tested whether endogenous PDGF-B expression in human skin xenotransplants leads to changes in the expression of alpha5 and alpha2 integrin subunits and whether integrin overexpression leads to PDGF-related changes in the skin. In vitro, transduction of fibroblasts with PDGF-B or the integrin alpha5 subunit stimulated multilayered growth and spindle-type morphology, both markers of mesenchymal cell transformation. In vivo, PDGF-B transduction of the human dermis was associated with up-regulation of collagen and fibronectin synthesis, increases in alpha5 and alpha2 integrin subunit expression, vessel formation, and proliferation of fibroblasts, keratinocytes, and pericytes. A similar stromal response was induced when alpha5 and alpha2 integrin subunits were overexpressed in the human dermis, suggesting that integrins play a major role in the induction of a transformed phenotype of fibroblasts by PDGF-B.

Signals controlling the expression of PDGF

PDGF is an important polypeptide growth factor that plays an essential role during early vertebrate development and is associated with tissue repair and wound healing in the adult vertebrate. Moreover, PDGF is thought to play a role in a variety of pathological phenomena, such as cancer, fibrosis and atherosclerosis. PDGF is expressed as a dimer of A and/or B chains, the precursors of which are encoded by two single copy genes. Although the PDGF genes are expressed coordinately in a number of cell types, they are independently expressed in a majority of cell types. The expression of either PDGF gene can be affected by very diverse extracellular stimuli and the type of response is dependent on the cell type that is exposed to the stimulus. Expression of the PDGF chains can be modulated at every imaginable level: by regulating accessibility of the transcription start site, by varying the transcription initiation rate, by using alternative transcription start sites, by alternative splicing, by using alternative polyadenylation signals, by varying mRNA decay rates, by regulating efficiency of translation, by protein modification, and by regulating secretion. Even upon secretion, the activity of PDGF can be modulated by non-specific or specific PDGF-binding proteins. This review provides an overview of the cell types in which the PDGF genes are expressed, of the factors that are known to affect the expression of PDGF, and of the various levels at which the expression of PDGF genes can be regulated.

Human malignant melanoma. A genetic disease?

BACKGROUND

Human hereditary malignant melanoma, comprising 5% of all cases of malignant melanoma, occurs in association with other malignancies, predominantly in families with dysplastic nevus syndrome. Additionally, higher incidences of malignant melanoma have been reported in individuals with genetic disorders such as ataxia telangiectasia and xeroderma pigmentosum. The results and observations as reported in the literature on the involvement of oncogenes and chromosomal aberrations in the development of malignant melanoma are reviewed and compared with the authors' own experimental and clinical experience.

RESULTS

Numerous chromosomal regions, as on chromosomes 1 and 9, were altered. The long arm of chromosome 6 was affected in 60% of melanomas. Introduction of a normal copy of chromosome 6 resulted in loss of tumorigenicity in vitro. True melanoma genes were evident in two animal models: the Sinclair swine and the teleost fish Xiphophorus. In the Xiphophorus system, the crossing-conditioned elimination of a tumor suppressor gene led to the uncontrolled activity of a dominantly acting oncogene in certain hybrids. The causative oncogene, Xmrk, encodes a receptor tyrosine kinase closely related to human epidermal growth factor receptor (EGFR). Among the numerous studied human oncogenes, mutations in the extensively investigated ras family are the result rather than the cause of malignant transformation. High expression of nuclear oncogenes simply may be a common feature of rapidly dividing cells. The receptor tyrosine kinase EGFR may be involved in late stage melanoma; the human exon with homology to Xmrk shows elevated transcription levels in 80% of human melanoma metastases. Deletions of the tumor suppressor gene MTS 1 may be important for melanoma formation, whereas deletions of p53 appear to be of minor relevance.

CONCLUSION

Scientific progress in treating and diagnosing malignant melanoma will largely depend on experimental approaches to define relevant genetic changes by functional analysis rather than descriptive phenomenology and correlative observations.

Malignant schwannoma in a case of type 1 neurofibromatosis with decreased immunoreactivity of smooth muscle alpha-actin in tumor vessels

A malignant schwannoma in the left calf of a 37-year-old man with type 1 neurofibromatosis is herein reported. Since it is known that capillaries in benign neurofibromas are accompanied by hypertrophic pericytes expressing an abundant amount of smooth muscle alpha-actin (SMAA), we examined the immunohistochemical reactivity of SMAA within this malignant tumor and then compared it with that in surrounding benign areas. In the nests of malignant cells, decreased SMAA staining was found in the capillary walls. In the benign tissues around the malignant tumor, various extents of SMAA could be visualized in the vessels and myofibroblasts. Platelet-derived growth factor (PDGF) was also detected in the tumor, suggesting that cytokines secreted by malignant cells may have an influence on the expression of SMAA as well as on the alteration of the structure of blood vessels.