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TGF beta 1 and TGF beta 2 are potential growth regulators for medulloblastomas, primitive neuroectodermal tumors, and
M T Jennings1, I T Kaariainen, L Gold
1Department of Neurology, Vanderbilt University, Nashville, TN 37232-3375.
Abstract:
Our previous investigations of transforming growth factor types beta 1 and beta 2 (TGF beta s) showed negative or positive autocrine growth regulation of gliomas in vitro. Near-diploid gliomas were inhibited by the TGF beta s, whereas a stimulatory response correlated with progressive anaplasia and karyotypic divergence. We have tested the hypothesis that cytogenetic aberrations may be associated with conversion of TGF beta autoregulation from inhibitory to stimulatory among other cultured neuroectodermal tumors. Anchorage-independent growth and karyotypic aberrations supported the malignant nature in vitro of two medulloblastoma (MBL), two primitive neuroectodermal tumor (PNET), and two ependymoma (EPD) cultures. Transforming growth factor type beta 1 and/or TGF beta 2 RNA was evident by Northern blot analysis among these cell cultures. By radioreceptor assay active TGF beta was present in conditioned medium in concentrations of 0 to 14 ng/mL, whereas the total amount of active and latent TGF beta secreted was in the range of 3 to 118 ng/mL. Expression of the TGF beta radioreceptor (TGF beta-R) types I and II was shown by cross-linking assay. Responses to exogenous TGF beta were determined by [3H]-thymidine incorporation, cell counts, and anchorage-independent clonogenicity. Exogenous TGF beta was growth inhibitory for the near-diploid MBL, PNET, and EPD in vitro, as well as antagonistic to the mitogenic effect of epidermal growth factor (EGF) and insulin. In contrast, MBL, PNET, and EPD with a hyperdiploid subpopulation were stimulated to proliferate in monolayer culture or soft agar by TGF beta 1 and TGF beta 2. The growth response did not correlate with TGF beta-R type. Autocrine regulation was supported by antibody neutralization experiments performed with quiescent cells in the absence of exogenous TGF beta. Anti-TGF beta antisera enhanced the growth of TGF beta-inhibited cultures, whereas the TGF beta-stimulated cultures were inhibited by the antisera. Karyotypic divergence seemed to predict response as MBL, PNET, and EPD with hyperdiploid elements exhibited autocrine TGF beta-stimulation. In contrast, the near-diploid cultures were inhibited by the TGF beta s. By analogy with the gliomas, conversion of TGF beta autocrine regulation from inhibition to stimulation may be a late progression marker of anaplasia among MBL, PNET, and EPD. Secretion of this TGF, which serves both as a mitogen and immunosuppressive agent may contribute to the adverse prognosis of hyperdiploid neuroectodermal neoplasms of the central nervous system (CNS).
Insights
Transforming growth factor beta (TGF-β) differentially regulates neuroectodermal tumor growth. Near-diploid tumors are inhibited, while hyperdiploid tumors show TGF-β-stimulated proliferation, indicating a progression marker.
Area of Science:
- Oncology
- Cell Biology
- Molecular Biology
Background:
- Transforming growth factor beta (TGF-β) exhibits dual roles in glioma growth regulation, inhibiting near-diploid cells and stimulating anaplastic variants.
- Cytogenetic aberrations are hypothesized to influence the conversion of TGF-β autocrine signaling from inhibitory to stimulatory in neuroectodermal tumors.
Purpose of the Study:
- To investigate the role of cytogenetic aberrations in mediating TGF-β autocrine signaling conversion in medulloblastoma (MBL), primitive neuroectodermal tumor (PNET), and ependymoma (EPD) cell cultures.
- To determine the differential growth responses of MBL, PNET, and EPD to TGF-β based on their cytogenetic profiles.
Main Methods:
- Cultured MBL, PNET, and EPD cells were analyzed for anchorage-independent growth and karyotypic aberrations.
- TGF-β RNA expression was assessed by Northern blot, and active/latent TGF-β levels were quantified by radioreceptor assay.
- TGF-β receptor expression was evaluated by cross-linking assays, and cellular responses to exogenous TGF-β were measured via [3H]-thymidine incorporation, cell counts, and soft agar clonogenicity.
- Autocrine regulation was assessed using anti-TGF-β antisera neutralization experiments.
Main Results:
- Malignant neuroectodermal tumor cell cultures (MBL, PNET, EPD) exhibited anchorage-independent growth and karyotypic aberrations.
- Exogenous TGF-β inhibited near-diploid MBL, PNET, and EPD, while stimulating hyperdiploid variants.
- Autocrine TGF-β signaling was confirmed; near-diploid cultures showed inhibition, and hyperdiploid cultures displayed stimulation, correlating with karyotypic divergence.
- TGF-β receptor expression levels did not correlate with growth response.
Conclusions:
- Cytogenetic divergence, particularly the presence of hyperdiploid elements, predicts a switch from TGF-β-mediated growth inhibition to stimulation in MBL, PNET, and EPD.
- This conversion of TGF-β autocrine regulation may serve as a late-stage anaplasia marker in these CNS neuroectodermal neoplasms.
- TGF-β's dual role as a mitogen and immunosuppressive agent could contribute to the poor prognosis of hyperdiploid neuroectodermal tumors.