BMP-2 Variants in Breast Epithelial to Mesenchymal Transition and Microcalcifications Origin

Abstract

This study aims to investigate the possible different roles of the BMP-2 variants, cytoplasmic and nuclear variant, in both epithelial to mesenchymal transition and in microcalcifications origin in human breast cancers. To this end, the in situ expression of cytoplasmic and nuclear BMP-2 was associated with the expression of the main epithelial to mesenchymal transition biomarkers (e-cadherin and vimentin) and molecules involved in bone metabolisms (RUNX2, RANKL, SDF-1) by immunohistochemistry. In addition, the expression of cytoplasmic and nuclear BMP-2 was associated with the presence of microcalcifications. Our data showed a significant association among the number of cytoplasmic BMP-2-positive cells and the number of both vimentin (positive association) and e-cadherin (negative association) positive breast cells. Conversely, no associations were found concerning the nuclear BMP-2-positive breast cells. Surprisingly, the opposite result was obtained by analyzing the variants of BMP-2 and both the expression of RANKL and SDF-1 and the presence of microcalcifications. Specifically, the presence of microcalcifications was related to the expression of nuclear BMP-2 variant rather than the cytoplasmic one, as well as a strong association between the number of nuclear BMP-2 and the expression of the main breast osteoblast-like cells (BOLCs) biomarkers. To further corroborate these data, an in vitro experiment for demonstrating the co-expression of nBMP-2 and RANKL or vimentin or SDF-1 in breast cancer cells that acquire the capability to produce microcalcifications was developed. These investigations confirmed the association between the nBMP-2 expression and both RANKL and SDF-1. The data supports the idea that whilst cytoplasmic BMP-2 can be involved in epithelial to mesenchymal transition phenomenon, the nuclear variant is related to the essential mechanisms for the formation of breast microcalcifications. In conclusion, from these experimental and translational perspectives, the complexity of BMP-2 signaling will require a detailed understanding of the involvement of specific BMP-2 variants in breast cancers.

Secretion of BMP-2 by tumor-associated macrophages (TAM) promotes microcalcifications in breast cancer

“…Our studies, amongst others, have presented robust evidence that breast cancer with microcalcifications is associated with poor clinical outcome [5,[21][22][23][24][25][26][27][28] and BMP-2 is upregulated in tissues with microcalcifications [3][4][5]. Based on the information currently available in the literature, BMP-2 is believed to be mainly secreted by cells in the tumor microenvironment, but not the breast cancer tumor cells themselves [29].…”

“…Currently, bone morphogenetic proteins 2 (BMP-2) has been implicated to play a role in the formation of microcalcifications. BMPs are growth factors of the TGF-β super family and BMP-2 is a specific and key regulator of osteoblast-like cells [3][4][5]. Studies have shown that BMP-2 can induce breast cancer cells to acquire osteoblastic characteristics, leading to the formation of microcalcifications [6].…”

Analysis of genomics and immune infiltration patterns of epithelial-mesenchymal transition related to metastatic breast cancer to bone

“…Bone morphogenetic proteins (BMPs) are important members of the TGF-β superfamily. At present, more than 20 BMPs have been discovered, and their biological functions are very extensive, including promoting bone and cartilage production, regulating cell proliferation and differentiation, and regulating the growth and development of various organs [18] , [19] , [20] , [21] , [22] , [23] . Studies have found that BMP-2 can activate Smad-independent pathways in tumor cells, including in the cancers of the breast, stomach, colon, and pancreas; for example, the PI3K/Akt signaling pathway to promote tumor cell invasion and metastasis [24] .…”

“…In addition, rhBMP-2 induces EMT in three BC cell lines (MCF-7, MDA-MB-231, and mouse BC cell line 4T1) and enhances cell migration and invasion ability both in vivo and in vitro [19 , 22] . Aberrant expression of BMP-2 has been observed in various tumors and is known to be closely related to EMT induction and tumor invasion [ [18] , [19] , [20] , 22 , 23] .…”

Molecular Aspects and Prognostic Significance of Microcalcifications in Human Pathology: A Narrative Review

“…Besides, a recent study displayed a correlation between the presence of BOLCs and the development of bone metastatic lesions within five years from histological diagnosis [ 28 , 57 ]. Li Zhang et al discovered that the tumor tissue produces BMP-2 locally through autocrine or paracrine ways, which combines with related receptors and enters the nucleus, acts at the target gene, and then regulates RUNX2, OPN, and other bone matrix proteins to form a microenvironment of calcium and phosphorus deposits in the tumor tissue, resulting in the formation of microcalcifications [ 51 ].…”