A novel function for the nm23-H1 gene: overexpression in human breast carcinoma cells leads to the formation of basement membrane and growth arrest.
BACKGROUND
We have developed a culture system using reconstituted basement membrane components in which normal human mammary epithelial cells exhibit several aspects of the development and differentiation process, including formation of acinar-like structures, production and basal deposition of basement membrane components, and production and apical secretion of sialomucins. Cell lines and cultures from human breast carcinomas failed to recapitulate this process. The data indicate the importance of cellular interactions with the basement membrane in the regulation of normal breast differentiation and, potentially, its loss in neoplasia.


OBJECTIVE
Our purpose was to use this assay to investigate the role of the putative metastasis suppressor gene nm23-H1 in mammary development and differentiation.


METHODS
The metastatic human breast carcinoma cell line MDA-MB-435, clones transfected with a control pCMVBamneo vector, and clones transfected with pCMVBamneo vector containing nm23-H1 complementary DNA (the latter of which exhibited a substantial reduction in spontaneous metastatic potential in vivo) were cultured within a reconstituted basement membrane. Clones were examined for formation of acinus-like spheres, deposition of basement membrane components, production of sialomucin, polarization, and growth arrest.


RESULTS
In contrast to the parental cell line and control transfectants, MDA-MB-435 breast carcinoma cells overexpressing Nm23-H1 protein regained several aspects of the normal phenotype within reconstituted basement membrane. Nm23-H1 protein-positive cells formed organized acinus-like spheres, deposited the basement membrane components type IV collagen and, to some extent, laminin to the outside of the spheres, expressed sialomucin, and growth arrested. Growth arrest of Nm23-H1 protein-positive cells was preceded by and correlated with formation of a basement membrane, suggesting a causal relationship.


CONCLUSIONS
The data indicate a previously unidentified cause-and-effect relationship between nm23-H1 gene expression and morphological-biosynthetic-growth aspects of breast differentiation in this model system.


CONCLUSIONS
While the basement membrane microenvironment is capable of directing the differentiation of normal human breast cells, neoplastic transformation abrogates this relationship, suggesting that intrinsic cellular events are also critical to this process. The data identify nm23-H1 gene expression as one of these events, suggesting an important role in the modulation of cellular responsiveness to the microenvironment. The data also identify previously unknown growth inhibitory effects of nm23-H1 gene overexpression.
Howlett
A R
AR
Division of Life Sciences, Lawrence Berkeley Laboratory, University of California, Berkeley 94720.
Petersen
O W
OW
Steeg
P S
PS
Bissell
M J
MJ
D000818:Animals; D001485:Basement Membrane / Q000378:metabolism; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002455:Cell Division / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D016147:Genes, Tumor Suppressor / Q000502:physiology*; D006801:Humans; D007150:Immunohistochemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D020559:Monomeric GTP-Binding Proteins; D054778:NM23 Nucleoside Diphosphate Kinases; D009701:Nucleoside-Diphosphate Kinase; D014157:Transcription Factors / Q000502:physiology*; D014162:Transfection; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000235:genetics*
D054778:NM23 Nucleoside Diphosphate Kinases; D014157:Transcription Factors; C517938:NME1 protein, human; C517939:Nme1 protein, mouse; D009701:Nucleoside-Diphosphate Kinase; D020559:Monomeric GTP-Binding Proteins