Genetic integrity of transforming growth factor β (TGF‐β) receptors in cervical carcinoma cell lines: loss of growth sensitivity but conserved transcriptional response to TGF‐β

Abstract

Transforming growth factor ␤ (TGF-␤) exerts an inhibitory effect on the growth of most epithelial cell types, and the loss of responsiveness to this growth inhibition has been implicated in the development of a variety of human cancers. The genetic alteration of TGF-␤ receptors is known to play a critical role in this escape from growth regulation. We asked whether there is a correlation between TGF-␤ sensitivity and the genetic status of TGF-␤ type I and type II receptors (RI and RII, respectively) in human cervical carcinoma cell lines. Among 8 cell lines examined, 3 (ME-180, C-33A and HeLaS3) showed resistance to TGF-␤ and 3 (SiHa, CaSki and HeLa229) showed minimal response to the growth inhibitory effect of TGF-␤; the other cell lines (HeLa and HT-3) were sensitive. Northern blot analysis revealed that the RII mRNA was not expressed in 2 TGF-␤-resistant cell lines (ME-180 and C-33A) but was expressed in the other cell lines. Southern blot analysis of RI and RII revealed a homozygous deletion of the entire TGF-␤ RII gene in the cell line ME-180. We then asked whether the other TGF-␤-resistant or refractory cell lines had microsatellite instability and/or poly-adenine tract mutations of RII. We also checked for point mutations in the individual exons of the entire RII using polymerase chain reaction-single-strand conformational polymorphism (PCR-SSCP). Although C-33A exhibited poly-adenine microsatellite instability, its RII gene showed no signs of mutation. The molecular integrity of the TGF-␤ receptors in all cell lines, except ME-180 and C-33A, could be confirmed by examining the distinct transcriptional induction of plasminogen activator inhibitor-1 (PAI-1), p21 WAF1/CIP1 and, in some cases, the accompanying downregulation of c-myc in response to TGF-␤. Our observations, taken together, indicate that inactivation of the RII contributes to the resistance to TGF-␤ of some cervical carcinoma cell lines. Loss of or attenuated sensitivity to TGF-␤ growth inhibition in other cells may be attributed to the disruption of distal components in the TGF-␤ signal pathway, but not to the receptor system. Int.

Invasion and metastasis of a mammary tumor involves TGF-? signaling

“…These findings are in concordance with those of others that have identified functional receptors in TGF-␤ growth resistant cancers such as glioma 33 , melanoma 34 and cervical carcinoma. 35 The intactness of Smadmediated gene transcription in the 4T1 mammary tumor cell line is similar to that reported in human melanoma cells in which Smadmediated gene transcription was shown to be independent of cell proliferation. 34 The TGF-␤-induced morphological changes that we observed in 4T1 mammary tumor cells are consistent with those reported by others in transformed murine mammary epithelial cells, 15 murine colon cancer cells 14 and skin carcinoma cells 16 and have been correlated with metastatic potential.…”

Mechanisms of decreased expression of transforming growth factor-beta receptor type I at late stages of HPV16-mediated transformation

“…For example, Kang et al . [23] reported a homologous deletion of the entire TGF-β RII gene in the cervical carcinoma cell line ME-180. However, 7 other cervical cancer cell lines studied that showed resistance or sensitivity to the growth inhibitory effects of TGF-β carry no genetic changes in TGF-β RI or TGF-β RII [23].…”

“…[23] reported a homologous deletion of the entire TGF-β RII gene in the cervical carcinoma cell line ME-180. However, 7 other cervical cancer cell lines studied that showed resistance or sensitivity to the growth inhibitory effects of TGF-β carry no genetic changes in TGF-β RI or TGF-β RII [23]. This is consistent with our results using Southern blot analysis, where we failed to find any gross structural alterations in TGF-β RI during in vitro progression [14].…”

“…Since our previous studies [14] as well as those discussed above [23-25] suggested that reduced expression of TGF-β RI in HKc/DR was unlikely linked to gross structural alterations of the receptor gene, we explored whether mutations in the promoter of TGF-β RI gene or receptor methylation may lead to altered TGF-β RI expression. Hypermethylation of the TGF-β RI gene in human gastric cancer cell lines [18] and of the TGF-β RII gene in murine renal cell carcinoma cells [26] have been correlated with a loss of receptor expression and TGF-β resistance.…”

A cell‐based high‐throughput assay for screening inhibitors of human papillomavirus‐16 long control region activity

“…Next we studied the effect of IL-4 and IL-13 on the expression of E6 and E7 genes in the CaSki cell line. Since TGF-β1 is a well-known inhibitor of HPV-16 LCR activity and its receptor is expressed on CaSki cells (24), it was also included as a reference in this set of experiments. To this aim, the cells were treated with 50 ng/ml of cytokines for 24 h, and E6 and E7 mRNA levels were determined by real-time RT-PCR.…”