Enhanced tumorigenesis and reduced transforming growth factor-beta type IIreceptor in lung tumors from mice with reduced gene dosage of transforminggrowth factor-beta 1
Y. Kang et al., Enhanced tumorigenesis and reduced transforming growth factor-beta type IIreceptor in lung tumors from mice with reduced gene dosage of transforminggrowth factor-beta 1, MOL CARCINO, 29(2), 2000, pp. 112-126
To elucidate the role of transforming growth factor-beta1 (TGF-beta1) and t
he TGF-beta type II receptor (TGF-beta RII)as tumor-suppressor genes in lun
g carcinogenesis, we mated C57BL/6 mice heterozygous (HT) for deletion of t
he TGF-beta1 gene with A/J mice to produce AJBL6 TGF-beta1 HT progeny and t
heir wild-type (WT) littermates. Immunohistochemical staining, in situ hybr
idization, and northern blot analyses showed lower staining and hybridizati
on for TGF-beta1 protein and mRNA, respectively, in the lungs of normal HT
mice versus WT mice. Competitive reverse transcription-polymerase chain rea
ction (CRT-PCR) amplification showed the level of TGF-beta1 mRNA in the lun
gs of HT mice to be fourfold lower than the level in WT lung. When challeng
ed with ethyl carbamate, lung adenomas were detected in 55% of HT mice by 4
mo but only in 25% of WT littermates at this time. Whereas all HT mice had
adenomas by 6 mo, it was not until 10 mo before all WT mice had adenomas.
After 12 mo, the average number of adenomas was fivefold higher in HT lungs
than in WT lungs. Most dramatic was the appearance of lung carcinomas in H
T mice 8 mo before they were visible in WT mice. Thus, the AJBL6 TGF-beta1
HT mouse provides an excellent model system to examine carcinogen-induced l
ung tumorigenesis by increasing progressive lesion incidence and multiplici
ty relative to their WT littermates. Immunohistochemical staining showed ex
pression of the TGF-beta type I receptor (TGF-beta RI) at moderate to stron
g levels in lung adenomas and carcinomas in HT and WT mice. In contrast, wh
ereas weak immunostaining for TGF-beta RII was detected in 67% of HT carcin
omas at 12 mo, only 22% of WT carcinomas showed weak staining for this prot
ein. individual lung carcinomas showing reduced TGF-beta RII expression and
adjacent normal bronchioles were excised from HT lungs using laser capture
microdissection, and CRT-PCR amplification of the extracted RNA showed 12-
fold less TGF-beta RII mRNA in these carcinomas compared with bronchioles.
Decreasing TGF-beta RII mRNA levels occurred with increasing tumorigenesis
in lung hyperplasias, adenomas, and carcinomas, with carcinomas having four
fold and sevenfold lower levels of TGF-beta RII mRNA than adenomas and hype
rplasias, respectively. These data show enhanced ethyl carbamate-induced lu
ng tumorigenesis in AJBL6 HT mice compared with WT mice, suggesting that bo
th TGF-beta1 alleles are necessary for tumor-suppressor activity. Reduction
of TGF-beta RII mRNA expression in progressive stages of lung tumorigenesi
s in HT mice suggests that loss of TGF-beta RII may play an important role
in the promotion of lung carcinogenesis in mice with reduced TGF-beta1 gene
dosage when challenged with carcinogen. Mol. Carcinog. 29:112-126, 2000. P
ublished 2000 Wiley-Liss. Inc.(dagger).