The interactions between luminal and myoepithelial cells determine the in vivo and in vitro malignant properties of a murine mammary tumor

MARTIN A. KRASNAPOLSKI; MARIA J. VELOSO; ALEJANDRO J. URTREGER; GABRIEL FISZMAN; MIRIAM J. DIAMENT; SLOBODANKA M. KLEIN; ANA MARÍA EIJAN; ELISA D. BAL DE KIER JOFFÉ

Anaheim, EEUU.

Congreso; 96th Annual Meeting of the American Association for Cancer Research (AACR); 2005

American Association for Cancer Research (AACR)

M38, a spontaneous murine mammary adenocarcinoma with papillary differentiation is metastatic to lung and lymph node. M38 is composed by two different cell types: luminal epithelial cells (LEP) and myoepithelial cells (MEP). To analyze M38´s malignant behaviour we derived different cell lines: LM38-LP (MEPs and LEPs), LM38-HP (mainly epithelial-like cells with some MEPs) and LM38-D2 (MEP clone). When inoculated into BALB/c mice, LM38-LP behaved identically as the parental tumor, while LM38-HP and LM38-D2 rendered slower-growing- and less-metastatic-tumors showing that the metastatic phenotype is absolutely dependent on the presence of both cell types. Cytogenetic analysis was performed to establish whether a hierarchical relationship existed among the different cell lines. All cell lines were aneuploid. LM38-LP´s main subpopulation was hypertetraploid (MEP cells) and the LEP one was hypotriploid. 76% of LM38-HP cells were hypotriploid with only 18% of hypertetraploid metaphases. Almost every cell in LM38-D2 (98%) was hypertetraploid. Two chromosomic markers were found in every cell type and, besides, novel alterations were also present in LM38-HP cells. To study whether differences in the malignant behavior were associated with cells susceptibility to stress, cell lines were exposed to serum deprivation or to doxorubicin, and the viability was assessed by the MTS assay. LM38-LP and LM38-D2 cells were significantly more resistant than LM38-HP. As angiogenesis is a very important step in the metastatic cascade, we compared the proangiogenic capacities of the different cell lines by an in vivo assay. Only LM38-LP induced the formation of a high number of vessels. This observation could be associated with a higher basal NO production by this cell line. To study whether we could recover the in vivo malignant behavior shown by the bi-cellular LM38-LP cell line, we inoculated s.c. different proportions of LM38-HP and LM38-D2, with or without a 36 h co-culture. Although we could not completely restore the papillary histology or the lymph node dissemination ability, the co-cultured cells showed an increased tumor growth rate and lung metastatic ability.The above studies suggest the existence of a bipotential progenitor cell capable of differentiating into malignant LEP and MEP cells, which interaction seems to be mandatory to the ability to grow and metastasize the lung. These properties may be explained by the diminished sensitivity to stress in the presence of MEP cells, and the enhanced proangiogenic capacity probably related to an enhanced NO production.