Mammary gland cells

Laminins have both overlapping and unique functions in the mammary gland tissue

Mammary ducts consist of an epithelial layer with a basal connection to a single layer of myoepithelial cells. The duct is encircled by a basement membrane sheet that is intimately connected with the myoepithelial cells (Fata, 2003). The mammary basement membrane mainly contains laminin isoforms 111, 332, 511, 521 and collagen IV. Changes in the basement membrane laminin composition influence stem cell maintenance and mammary development, but also plays a role during aging and in aging-related diseases, such as cancer (Hu, 2017; Fata 2003). The extracellular matrix not only helps to support mammary basic structure but also serves as a communicating bridge between mammary epithelia and their local and global environment throughout development. The major integrin receptors in the mammary gland are α3β1, α6β1 and α6β4 and the interaction between mammary epithelial cells and their extracellular matrix is crucial in the development and function of the tissue, affecting cell survival, polarity, proliferation, differentiation, adhesion, and migration (Hu, 2017; Muschler, 2010; Fata, 2003).

Laminin 111 is important for the initiation of mammary gland development, for ductal elongation and end bud persistence

End buds are surrounded by a basement membrane that is rich in laminin 111 and collagen IV. Blocking laminin 111 or β1 integrins specifically and dramatically reduced both the number of end buds per gland and the extent of the mammary ductal network (Klinowska, 1999). Laminin 111 and laminin 332 are suggested to be involved in the initiation of mammary gland development, where laminin 111 has been shown to be critical for ductal elongation and end bud persistence (Chia, 2007; Hu, 2017; Muschler, 2010). Laminin 111 is also important for mammary epithelial cells to form polarized acinar structures, express b-Casein and permit prolactin receptor signaling (Hu, 2017; Muschler, 2010).

Laminin 511 and laminin 521 control submandibular gland epithelial morphogenesis and is required for correct epithelial cell organization and lumen formation

Laminin 511 is abundant in the vasculature of normal human mammary glands (Chia, 2007). Published results show that laminin 511 is not essential for gland initiation, but plays an important role in the initial cleft formation and epithelial morphogenesis. Laminin 511 is also necessary for sublingual gland formation and later in development, is required for epithelial cell organization and lumen formation (Rebustini, 2007; Hu, 2017; Muschler, 2010). In submandibular glands, laminin 511 and laminin 111 are present in epithelial clefts but during epithelial morphogenesis as branching begins, laminin 511 expression increases while laminin 111 decreases. The data suggest that submandibular gland epithelial morphogenesis is controlled by α5-chain laminins (laminin 511 and 521), regulated via β1 integrin signaling. Laminin 511 also regulates FGFR expression, independent of laminin 111, which reciprocally regulates the expression of the laminin α5 subunit (Rebustini et al., 2007).

Laminin 511 and 521 promotes breast cancer cell migration and invasion

The laminin 511 and 521 isoforms are expressed in high levels in breast tumors (Chia, 2007) and are suggested to play an autocrine role in mammary cancer progression (Chia, 2007). Laminin 111 and laminin 332 are both down-regulated in most advanced breast tumors, suggesting a tumor-suppressive role (Muschler, 2010). On the contrary, laminin 511 acts as a functional substrate, regulating breast cancer metastasis. Laminin 511 is a potent adhesive substrate for both murine and human breast carcinoma cells and promotes strong haptotactic responses in metastatic lines, largely mediated by the α3 integrin (Chia, 2007; Kusuma, 2011). Chia et al. propose that laminin 511 contributes during the process of metastasis via the attachment of breast tumor cells to blood vessel walls. These results are in accordance with a publication by Chang et al. where the authors show that breast cancer stem cells produce alpha-5 laminin matrix that promotes self-renewal and tumor initiation via α6β1 integrin interaction. α5 chain laminins also activate the Hippo transducer TAZ which in turn regulates the transcription of the α5 laminin subunit, establishing a positive feedback loop that contributes to stemness in breast cancer (Chang, 2014). 

Protocol:

Breast tumor cell migration and invasion assay