Hox gene expression in human small‐cell lung cancers xenografted into nude mice

Abstract

Transcription factors are crucial to an understanding of the molecular basis of neoplasia. Horneobox‐containing genes are a family of transcriptional regulators encoding DNA‐binding ho‐meodomains, involved in the control of normal development. Class‐1 human homeobox‐containing genes (HOX genes) display a peculiar chromosomal organization, perhaps directly related to their function. Aberrant expression of homeobox‐genes has been associated with both morphological abnormalities and oncogenesis. We have recently observed that alterations in HOX gene expression are detectable in kidney and colon cancer when compared to the corresponding normal organs. Here we have analyzed the expression of HOX genes in primary and metastatic human small‐cell lung cancer (SCLC) xenografted in nude mice, in order to investigate whether HOX gene expression correlates with the histology and stage of SCLC progression. The results show that different SCLCs display differential patterns of HOX gene expression. Furthermore, in SCLC, the number of actively expressed HOX genes might be substantially lower in metastatic cancers than in primary tumors. The alteration in HOX gene expression in SCLCs mainly concerns the HOX B and C loci. This finding suggests that downregulation of HOX genes may play a role in small‐cell lung cancer progression, possibly through their implication in tumor suppression.

Relationship between DNA methylation and gene expression of the HOXB gene cluster in small cell lung cancers

“…In contrast, SCLC-75 and SCLC-6 displayed dramatically different HOX gene patterns of expression: in SCLC-75, all but HOXB7 genes were expressed, whereas SCLC-6 expressed only HOXB3. Although the general trends remained the same as those published previously [15], slight differences in the expression patterns were observed: SCLC-6 now expressed HOXB3 but not HOXB4, SCLC-10 and SCLC-82 expressed HOXB6, and SCLC-75 no longer expressed HOXB7. These differences might be explained by different sensitivities between RT-PCR and Northern blot- HpaII (methylation-sensitive), several band patterns were observed: a band of about 1 kb was seen in SCLC-6, SCLC-10 and SCLC-82, but not in SCLC-75 which exhibited bands at 4 and 5.5 kb; SCLC-10, and to a much lesser extent SCLC-82, also contained longer fragments indicating the presence of methylated restriction sites.…”

“…The main characteristics of the xenografted SCLC used in this study have been reported elsewhere [15]. Briefly, human SCLC tissues, obtained through fibroscopy or surgical excision of tumors from patients with histologically confirmed diagnoses of SCLC, were xenografted into 6-8-week-old Swiss/athymic mice (IFFA-Credo, Lyon, France) by s.c. implantation.…”

“…Methylation was also studied in the same experimental conditions with methylation-sensitive restriction enzymes HhaI and BstUl. Eight probes of the 3' regions of the HOXB genes were previously used for gene-expression studies [15]. One probe of the 5' region of the HOXB4 gene was obtained from the American Type Culture Collection (ATCC 65146) [30].…”

“…After embryogenesis, HOX genes may continue to be transcribed according to a tissue-specific pattern of expression. In cancer, alterations of this pattern, as compared to the corresponding normal mature tissues, have been described [12][13][14][15][16][17][18][19][20][21]. However, few data are presently available on HOX gene regulation in adult tissues or on the mechanisms responsible for the changes observed in cancer cells.…”

“…In this study, we attempted to estimate the global methylation of the DNA along a HOX locus to search for a possible relationship between DNA methylation and HOX gene-expression patterns [15]. We took advantage of a panel of xenografted small-cell lung cancers (SCLC) to select cases with different expression patterns, thereby allowing expression-methylation cross-correlation studies.…”