nm23 has properties of a metastasis suppressor gene and also has been implicated in the control of response to transforming growth factor β1 (TGFβ1) by studies in melanoma cells. In this report, we have examined the role of nm23 in two HT29 colon carcinoma sublines at different stages in tumor progression with different responses to TGFβ1: the HD3 subline, which shows TGFβ1-induced growth arrest and differentiation; and the more invasive and tumorigenic U9 subline, which induces tumors 7-fold as large as those induced by HD3 cells with one-half the latency. Analysis by semiquantitative reverse transcription-polymerase chain reaction showed that antisense phosphorothiolated oligonucleotides to the nm23 initiation site (nm23 AS oligos) decreased nm23 mRNA levels 2-8-fold in HD3 and U9 cells when normalized to β-actin mRNA levels. However, a role for nm23 in TGFβ1- mediated responses could only be found in HD3 cells. nm23 AS oligos inhibited the differentiation property of cell adherence over 90% in HD3 cells, and this loss of adherence could be partially blocked by concurrent treatment with TGFβ1. In contrast, U9 cell adherence was not detectably altered by nm23 AS oligos, whether added in the presence or absence of TGFβ1. The TGFβ1-induced inhibition of HD3 cell proliferation was blocked by nm23 AS oligos, whereas the TGFβ1-induced proliferation of U9 cells was unaffected by nm23 AS oligos. TGFβ1 increases nm23 mRNA and protein levels in HD3 cells, which may explain the opposing effects of nm23 AS oligos and TGFβ1 in these cells. No mutation in the coding sequence of nm23 was detected in U9 cells to explain the lack of effects of nm23 AS oligos. nm23 mRNA and protein levels were similar in the two lines. We have recently shown that TGFβ1 induces two distinct signal transduction pathways in epithelial cells (Z. Yan et al., J. Biol. Chem., 269: 13231-13237, 1994), one leading to increased cell adherence and growth arrest in HD3 cells, with the other leading to increased invasion and tumorigenicity in U9 cells. The data in the current study indicate that nm23 functions only in the TGFβ1 signaling pathway leading to growth arrest and differentiation. After colon carcinoma cells have progressed to a more aggressive phenotype and use TGFβ1 to stimulate growth and invasion (S. Hsu, et al., Cell Growth and Diff., 5: 267-275, 1994), the second TGFβ1 signaling pathway is used which does not include nm23. Loss of nm23 function occurs in melanoma cells because of a decrease in expression level, whereas by this model in more aggressive colon carcinoma cells, loss of nm23 function occurs by use of an alternative TGFβ1 signaling pathway.
|Original language||English (US)|
|Number of pages||9|
|Journal||Cell Growth and Differentiation|
|Publication status||Published - Jan 1 1994|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology