Inactivation of the transforming growth factor β type II receptor in human small cell lung cancer cell lines

Abstract

Summary Transforming growth factor β (TGF-β) exerts a growth inhibitory effect on many cell types through binding to two types of receptors, the type I and II receptors. Resistance to TGF-β due to lack of type II receptor (RII) has been described in some cancer types including small cell lung cancer (SCLC). The purpose of this study was to examine the cause of absent RII expression in SCLC cell lines. Northern blot analysis showed that RII RNA expression was very weak in 16 of 21 cell lines. To investigate if the absence of RII transcript was due to mutations, we screened the poly-A tract for mutations, but no mutations were detected. Additional screening for mutations of the RII gene revealed a GG to TT base substitution in one cell line, which did not express RII. This mutation generates a stop codon resulting in predicted synthesis of a truncated RII of 219 amino acids. The nature of the mutation, which has not previously been observed in RII, has been linked to exposure to benzo[a]-pyrene, a component of cigarette smoke. Since RII has been mapped to chromosome 3p22 and nearby loci are often hypermethylated in SCLC, it was examined whether the lack of RII expression was due to hypermethylation. Southern blot analysis of the RII promoter did not show altered methylation patterns. The restriction endonuclease pattern of the RII gene was altered in two SCLC cell lines when digested with Sma1. However, treatment with 5-aza-2′-deoxycytidine did not induce expression of RII mRNA. Our results indicate that in SCLC lack of RII mRNA is not commonly due to mutations and inactivation of RII transcription was not due to hypermethylation of the RII promoter or gene. Thus, these data show that in most cases of the SCLC cell lines, the RII gene and promoter is intact in spite of absent RII expression. However, the nature of the mutation found could suggest that it was caused by cigarette smoking.

Variant alleles of TGFB1 and TGFBR2 are associated with a decreased risk of gastric cancer in a Chinese population

“…[36][37][38] However, the G-875A variant was the only common (minor allele frequency >0.05) variant ever found in the promoter region of TGFBR2, 29 which may be responsible for individual susceptibility to TGF-bRII-related cancers. Experimental studies showed that the introduction of an A for G at position 2875 enhanced the activity of TGFBR2 transcription in normal epithelial cells, and specific binding was seen with oligonucleotide probes including the 2875 position, which may explain the protective effect of the 2875A allele for gastric cancer.…”

Sequence-specific enhancer binding protein is responsible for the differential expression of ERT/ESX/ELF-3/ESE-1/jen gene in human gastric cancer cell lines: Implication for the loss of TGF-β type II receptor expression

“…These tumors possess reduced or undetectable levels of receptors for TGF-b. Several lines of evidence suggest that transcriptional repression of the TGF-b RII gene may be a major mechanism to inactivate TGF-b RII (Park et al, 1994;Kadin et al, 1994;Horie et al, 1998;Hougaard et al, 1999;Hahm et al, 1999). A series of Figure 6 Characterization of the strong positive element (7186 to 7177) of ERT promoter.…”

“…Frame shift mutations within a 10 bp polyadenine repeat present in the TGFb RII coding region frequently occur in cells with microsatellite instability or replication errors (RER+), leading to premature termination of the receptor protein Myero et al, 1995). In addition, it is reported that transcriptional repression of TGF-b RII gene may be another mechanism leading to TGF-b resistance (Park et al, 1994;Kadin et al, 1994;Horie et al, 1998;Hougaard et al, 1999). Transformation of cells by the product of the adenovirus E1A gene (Missero et al, 1991;Kim et al, 1997), or overexpression of cyclin D1 (Okamoto et al, 1994) in epithelial cells, has been associated with downregulation of TGF-b RII expression and TGF-b resistance.…”

Inhibition of Transforming Growth Factor-β Signaling in Normal Lung Epithelial Cells Confers Resistance to Ionizing Radiation

“…Lung tumors are known to harbor aberrant expression of RII and lack or contain mutations in Smad-4 expression (19,20). The finding that RII/Smad4 expression is low in many lung cancer cell lines raises the possibility that absence of RII/Smad4 expression may cause lack of response to TGF-β and this can play a critical role in resistance to chemotherapy and radiation.…”