Early induction of angiogenetic signals in gliomas of GFAP-v-src transgenic mice.
(1/494)
Angiogenesis is a prerequisite for solid tumor growth. Glioblastoma multiforme, the most common malignant brain tumor, is characterized by extensive vascular proliferation. We previously showed that transgenic mice expressing a GFAP-v-src fusion gene in astrocytes develop low-grade astrocytomas that progressively evolve into hypervascularized glioblastomas. Here, we examined whether tumor progression triggers angiogenetic signals. We found abundant transcription of vascular endothelial growth factor (VEGF) in neoplastic astrocytes at surprisingly early stages of tumorigenesis. VEGF and v-src expression patterns were not identical, suggesting that VEGF activation was not only dependent on v-src. Late-stage gliomas showed perinecrotic VEGF up-regulation similarly to human glioblastoma. Expression patterns of the endothelial angiogenic receptors flt-1, flk-1, tie-1, and tie-2 were similar to those described in human gliomas, but flt-1 was expressed also in neoplastic astrocytes, suggesting an autocrine role in tumor growth. In crossbreeding experiments, hemizygous ablation of the tumor suppressor genes Rb and p53 had no significant effect on the expression of VEGF, flt-1, flk-1, tie-1, and tie-2. Therefore, expression of angiogenic signals is an early event during progression of GFAP-v-src tumors and precedes hypervascularization. Given the close similarities in the progression pattern between GFAP-v-src and human gliomas, the present results suggest that these mice may provide a useful tool for antiangiogenic therapy research. (+info)
RB regulates the stability and the apoptotic function of p53 via MDM2.
(2/494)
The binding of RB to MDM2 is shown to be essential for RB to overcome both the antiapoptotic function of MDM2 and the MDM2-dependent degradation of p53. The RB-MDM2 interaction does not prevent MDM2 from inhibiting p53-dependent transcription, but the RB-MDM2 complex still binds to p53. Since RB specifically rescues the apoptotic function but not the transcriptional activity of p53 from negative regulation by MDM2, transactivation by wild-type p53 is not required for the apoptotic function of p53. However, an RB-MDM2-p53 trimeric complex is active in p53-mediated transrepression. These data link directly the function of two tumor suppressor proteins and demonstrate a novel role of RB in regulating the apoptotic function of p53. (+info)
Simultaneous alterations of retinoblastoma and p53 protein expression in astrocytic tumors.
(3/494)
The genetic alterations frequently involved in glial malignancies are in the tumor suppressor genes, Rb and p53. An altered Rb expression or p53 overexpression is thought to indicate defective tumor suppression and subsequently more aggressive tumors. Therefore, to assess the alterations in the conjoint expression of Rb and p53 proteins in formalin fixed paraffin embedded sections, 64 astrocytic tumors were studied (16 astrocytomas,7 gemistocytic astrocytomas, 19 anaplastic astrocytomas and 22 glioblastomas) using the avidin biotin immunoperoxidase technique. Fifty two cases (81.25%) were found to be positive for p53 protein. Seventeen of these showed aberrant heterogenous staining for pRb, of which 7 were glioblastomas. Only one case of astrocytoma showed aberrant expression of both p53 and Rb. Thus, of the 64 tumors, simultaneous aberrant expression of both p53 and Rb was seen in 21.9% of cases. This was more commonly observed among glioblastoma cases (7/22). No statistical difference was found between the survival rate of heterogenous pRb and p53 positivity in different grades of tumors. In glioblastomas, the survival rate appeared to be less in patients expressing heterogenous pRb, but this was not statistically significant. These results lead us to suspect that p53 and pRb pathways are inactivated, either through mutation or as part of the neoplastic process in astrocytic tumors. (+info)
RB-mediated suppression of spontaneous multiple neuroendocrine neoplasia and lung metastases in Rb+/- mice.
(4/494)
Alterations in pathways mediated by retinoblastoma susceptibility gene (RB) product are among the most common in human cancer. Mice with a single copy of the Rb gene are shown to develop a syndrome of multiple neuroendocrine neoplasia. The earliest Rb-deficient atypical cells were identified in the intermediate and anterior lobes of the pituitary, the thyroid and parathyroid glands, and the adrenal medulla within the first 3 months of postnatal development. These cells form gross tumors with various degrees of malignancy by postnatal day 350. By age of 380 days, 84% of Rb+/- mice exhibited lung metastases from C-cell thyroid carcinomas. Expression of a human RB transgene in the Rb+/- mice suppressed carcinogenesis in all tissues studied. Of particular clinical relevance, the frequency of lung metastases also was reduced to 12% in Rb+/- mice by repeated i.v. administration of lipid-entrapped, polycation-condensed RB complementary DNA. Thus, in spite of long latency periods during which secondary alterations can accumulate, the initial loss of Rb function remains essential for tumor progression in multiple types of neuroendocrine cells. Restoration of RB function in humans may prove an effective general approach to the treatment of RB-deficient disseminated tumors. (+info)
The presence of the Rb c-box peptide in the cytoplasm inhibits p210bcr-abl transforming function.
(5/494)
In order to test if the carboxyl terminal polypeptide of the Retinoblastoma (Rb) tumor suppressor protein, could be used to suppress the growth factor-independent growth phenotype of p210bcr-abl positive myeloid cells, we introduced a truncated form of the 3' end of the Rb cDNA encoding its last 173 amino acid residues (Rb C-box) which localize into the cytoplasm where the p210bcr-abl transforming protein is found, into myeloid cells (32D) which depends on the p210bcr-abl protein for IL3 growth factor-independent growth (32D-p210). The expression of the plasmid vectors carrying the Rb C-box cDNAs was shown to inhibit the abl tyrosine specific protein kinase activity of the p210(bcr-abl) oncoprotein and to suppress the IL3-independent growth phenotype of the 32D-p210 cells. The Rb C-box polypeptides did not suppress the growth of the untransfected 32D parental cell line in methylcellulose in the presence of IL3-conditioned medium. These results suggest that the cytoplasmic localization of the p210(bcr-abl) allows it to escape the effect of intranuclear proteins such as Rb which negatively regulate the p145(c-abl) kinase. (+info)
Chromosome 13q deletion mapping in pituitary tumors: infrequent loss of the retinoblastoma susceptibility gene (RB1) locus despite loss of RB1 protein product in somatotrophinomas.
(6/494)
Two recent studies have described allelic loss of an RB1 intragenic marker on chromosome 13q in aggressive and metastatic pituitary tumors that did not correlate with loss of pRB. The second report also showed that losses were more frequently associated with a more centromeric marker. Because both of these studies suggest the presence of another or other tumor suppressor genes (TSGs) on 13q, we carried out an allelotype analysis encompassing known and recently described TSG loci on 13q, together with immunohistochemical analysis of pRB. We analyzed 82 nonfunctional tumors and 53 somatotrophinomas subdivided into invasive and noninvasive cohorts. A significantly higher frequency of loss, at one or more of 13 markers, was evident in the invasive nonfunctional tumors (54%, 26 of 48) than in their noninvasive counterparts (29%, 10 of 34). An approximately equal frequency of loss was apparent in invasive (28%, 5 of 18) and noninvasive (31%, 11 of 35) somatotrophinomas at one or more markers. In those tumors harboring deletion, loss at two or more markers was more frequent in invasive nonfunctional tumors 65% (17 of 26) compared with 36% (4 of 11) of their noninvasive counterparts. In somatotrophinomas, 40% (2 of 5) of invasive tumors as compared with 64% (7 of 11) of noninvasive tumors had evidence of two or more deletions. In tumors showing loss at two or more loci, the majority showed large deletions; however, loss of the RB1 intragenic marker D13S153 was infrequent. In most cases, loss at individual markers was more frequent in invasive tumors than their noninvasive counterparts. A marker 3 cM telomeric to RB1 (D13S1319) showed the highest frequency of deletion in both invasive cohorts (29% of somatotrophinomas and 24% of nonfunctional tumors). Immunohistochemical analysis of pRB showed frequent loss in somatotrophinomas (27%, 9 of 33) in comparison with 4% (2 of 53) of non-functional tumors. Although loss of pRB did not correlate with loss of an intragenic marker or tumor grade, it was significantly associated with the somatotrophinoma subtype (P = 0.002). These data suggest that chromosome 13q is a frequent target for allelic deletion in pituitary tumors and point to another or other TSG loci in these regions. (+info)
Balancing proliferation and apoptosis in vivo: the Goldilocks theory of E2F/DP action.
(7/494)
Stimulation of both proliferation and apoptosis by E2F-1 provides a mechanistic basis for how E2F-1 functions as an oncogene and a tumor suppressor in vivo. In each normal tissue, a precise balance of proliferation versus apoptosis must be maintained, and in many tissues this appears to be controlled by E2F-1 levels. Presumably, variable expression of all E2F family members in each tissue dictates a tissue-specific sensitivity to loss or overexpression of any one family member. At sites where E2F-1 contributes mainly to proliferation and p53 levels remain low, loss of E2F-1 expression may lead to tissue atrophy and overexpression may lead to hyperplasia or tumors. Hence, E2F-1 would act as an oncogene. At other sites where E2F-1 levels induce p19, which stabilizes p53 leading to apoptosis, E2F-1 overexpression may lead to tissue atrophy and loss of expression may lead to hyperplasia or tumors. And thus, E2F-1 would act as a tumor suppressor. Perhaps it is the unique property of E2F-1 within the E2F family to stimulate both proliferation and apoptosis which makes it a bimodal switch that pRB must control so carefully. It is a delicate equilibrium that must be maintained throughout embryonic development and adult life. However, it is easy to envision that mutations which deregulate other E2F family members and which ultimately lead to changes in E2F-1 levels could lead to similar growth aberrations. In summary, although pRB interacts with numerous transcription factors, pRB minimally must restrain the E2F/DP transcription factor family to prevent the cell cycle from whirling onwards out of control. (+info)
Adenoviral-mediated gene transfer of a constitutively active form of the retinoblastoma gene product attenuates neointimal thickening in experimental vein grafts.
(8/494)
PURPOSE: Inappropriate or excessive vascular smooth muscle cell proliferation leads to the development of occlusive lesions in up to 50% of vein grafts. The purpose of this study was to test the hypothesis that induced overexpression of a cytostatic nonphosphorylatable form of the retinoblastoma protein (DeltaRb) would attenuate neointimal thickening in experimental vein grafts. METHODS: A replication-deficient adenovirus vector that encoded a nonphosphorylatable, constitutively active form of DeltaRb was constructed (AdDeltaRb) and contained an NH2-terminal epitope tag from the influenza hemagglutinin molecule (HA). Forty-eight male New Zealand white rabbits underwent surgical exposure of the external jugular vein for transfection with either 3 x 10(10) plaque-forming units/mL AdDeltaRb (n = 16), 3 x 10(10) plaque-forming units/mL control adenovirus (AdBglII, n = 15), or vehicle (n = 17) for 10 minutes at 120 mm Hg. After vector exposure, the vein was excised and interposed end-to-end into the carotid circulation. After 5 days, 12 grafts (four from each group) were excised and assayed for genomic DeltaRb DNA with the polymerase chain reaction or for hemagglutinin molecule expression and localization with immunohistochemistry. The remainder of the grafts (n = 36) were perfusion-fixed after 4 weeks, and 5 microm sections prepared for digital planimetric analysis. RESULTS: Polymerase chain reaction results identified the DeltaRb gene only in the grafts that were transfected with AdDeltaRb. Immunohistochemical analysis results revealed transgene expression in most of the endothelial cells and in many of the smooth muscle cells. After 4 weeks, the grafts that were exposed to AdDeltaRb exhibited a 22% reduction in neointimal thickness (vehicle, 77 +/- 7 microm; AdBglII, 75 +/- 5 microm; AdDeltaRb, 60 +/- 5 microm; P =.05), and medial thickness, luminal diameter, and other parameters were unchanged (medial thickness: vehicle, 72 +/- 10 microm; AdBglII, 85 +/- 7 microm; AdDeltaRb, 69 +/- 9 microm; P = NS; luminal diameter: vehicle, 4.5 +/- 0.2 mm; AdBglII, 4.4 +/- 0.2 mm; AdDeltaRb, 4.7 +/- 0.1 mm; P = NS). CONCLUSION: With this delivery system, adenoviral-mediated gene transfer is highly efficient and induced overexpression of DeltaRb leads to a reduction in vein graft neointimal thickening. (+info)