The mammary gland undergoes dynamic remodeling which requires cell proliferation in order to maintain the gland's form and function. Cell communication plays a critical role during proliferation. Here I show that Comma1D-βgeo (C1D) cells exhibit different rates of proliferation when grown in adherent versus non- adherent culture. The modulation of substrate attachment during culture presents different environments for C1D cell growth, altering the repertoire of adhesion molecules (AMs) which may affect proliferation. Data show that the CD24 subpopulations have differing proliferation potentials in the different culture conditions. Cells expressing CD24^low grown in adherent culture have a higher proliferation rate compared to CD24^high cells. Cells expressing CD24^high grown in non-adherent culture form more mammospheres compared to CD24^low cells. Intracellular analysis showed that C1D cells, along with phenotypes not yet identified in the mammary hierarchy, exhibit predominately basal cells (K5⁺αSMA⁺ and αSMA⁺). These basal phenotypes were expressed in cell subpopulations grown in adherent culture while subpopulations in non-adherent culture contained a variety of basal and luminal cells including progenitor populations (K5⁺, K5⁺ αSMA⁺, αSMA⁺, K5⁺K8⁺, and K8⁺). Microarray analysis revealed a common upregulated gene Sialophorin (Spn, CD43). Categorized by ontology as involved in adhesion and proliferation, sialophorin was upregulated in subpopulations demonstrating higher proliferation rates in both culture conditions (P < 0.05). Thought only to be present on hematopoietic cells, Spn is has been found to be highly expressed in primary breast tumors and their metastases, affecting proliferative capability. Here, Spn may also play an important role in normal mammary development by regulating the proliferation of mammary progenitor cells.

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