Cancer invasion and metastasis: Insights from murine pubertal mammary gland morphogenesis

Interactions between cancer cells and tumor-associated macrophages in tumor microenvironment

Tumor microenvironment (TME) refers to the local environment in which various cancer cells grow, encompassing tumor cells, adjacent non-tumor cells, and associated non-cellular elements, all of which collectively promote cancer occurrence and progression. As a principal immune component in the TME, tumor-associated macrophages (TAMs) exert a considerable influence on cancer behaviors via their interactions with cancer cells. The interactive loops between cancer cells and TAMs, including secretory factors derived from both cancer cells and TAMs, are crucial for the proliferation, stemness, drug resistance, invasion, migration, metastasis, and immune escape of various cancers. Cancer cells release paracrine proteins (HMGB1, AREG etc.), cytokines (IL-6, CCL2 etc.), RNAs (miR-21-5p, circPLEKHM1, LINC01812 etc.), and metabolites (lactic acid, succinate etc.) to regulate the polarization phenotype, mediator secretion and function of TAMs. In turn, mediators (TGF-β, IL-10, IL-6 etc.) from TAMs promote cancer progression. This review summarizes recent advancements in the interactive loops between cancer cells and TAMs in TME. Inhibiting the recruitment and M2 polarization of TAMs, reprogramming TAMs from M2 to M1 phenotype, blocking TAMs-mediated immunosuppression and immune escape, and combining with existing immunotherapy can target TAMs to overcome immunotherapy resistance in various cancers. The new breakthroughs lie in identifying effective targets for drug development, improving the drug delivery system to enhance the drug delivery efficiency, and adopting combined therapy. Interventions targeting secretory factors, cell surface receptors, intracellular signaling pathways, and metabolic modulation in the interactive loops between cancer cells and TAMs are expected to suppress cancer progression and improve therapeutic effects.

Multiple anti-tumor programs are activated by blocking BAD phosphorylation

The Bcl-2 family member BAD is a candidate disease modulator because it stimulates apoptosis in a cell context basis and inhibits cell migration during normal mammary gland morphogenesis. This activity depends on 3 key regulatory serines (S75, 99, 118) in the unphosphorylated state. Given that developmental programs are often hijacked in cancer, we hypothesized that BAD would impede breast cancer progression. We generated breast cancer mouse models representing loss-of-function or phosphorylation deficient mutations (PyMT-Bad-/- and PyMT-Bad3SA/3SA, respectively). Preventing BAD phosphorylation significantly decreased breast cancer progression and metastasis. The knock-out phenocopied the control PyMT-Bad+/+ suggesting that phosphorylated BAD protein was inert. Thus, the BAD3SA mutation unmasked latent anti-tumor activity. Indeed, transcriptomics showed PyMT-Bad3SA/3SA activated multiple anti-tumor programs including apoptosis, inflammation, cellular differentiation, and diminished cell migration. This anti-tumor effect associated with clinical survival of breast cancer patients whose tumors had high levels of unphosphorylated BAD. Kinase screens identified ERK as the major BAD kinase in breast cells, and ERK inhibition impeded tumoroid invasion. Our data suggest that unphosphorylated BAD modulates anti-tumor pathways that contribute to excellent patient prognosis. Thus, targeting ERK to dephosphorylate BAD may be an exciting therapeutic opportunity in the future.

Tspan protein family: focusing on the occurrence, progression, and treatment of cancer

The Tetraspanins (Tspan) protein family, also known as the tetraspanin family, contains 33 family members that interact with other protein molecules such as integrins, adhesion molecules, and T cell receptors by forming dimers or heterodimers. The Tspan protein family regulates cell proliferation, cell cycle, invasion, migration, apoptosis, autophagy, tissue differentiation, and immune response. More and more studies have shown that Tspan proteins are involved in tumorigenesis, epithelial-mesenchymal transition, thrombosis, tumor stem cell, and exosome signaling. Some drugs and microRNAs can inhibit Tspan proteins, thus providing new strategies for tumor therapy. An in-depth understanding of the functions and regulatory mechanisms of the Tspan protein family, which can promote or inhibit tumor development, will provide new strategies for targeted interventions in the future.

An Increase in HSF1 Expression Directs Human Mammary Epithelial Cells toward a Mesenchymal Phenotype

HSF1 is a well-known heat shock protein expression regulator in response to stress. It also regulates processes important for growth, development or tumorigenesis. We studied the HSF1 influence on the phenotype of non-tumorigenic human mammary epithelial (MCF10A and MCF12A) and several triple-negative breast cancer cell lines. MCF10A and MCF12A differ in terms of HSF1 levels, morphology, growth in Matrigel, expression of epithelial (CDH1) and mesenchymal (VIM) markers (MCF10A are epithelial cells; MCF12A resemble mesenchymal cells). HSF1 down-regulation led to a reduced proliferation rate and spheroid formation in Matrigel by MCF10A cells. However, it did not affect MCF12A proliferation but led to CDH1 up-regulation and the formation of better organized spheroids. HSF1 overexpression in MCF10A resulted in reduced CDH1 and increased VIM expression and the acquisition of elongated fibroblast-like morphology. The above-mentioned results suggest that elevated levels of HSF1 may direct mammary epithelial cells toward a mesenchymal phenotype, while a lowering of HSF1 could reverse the mesenchymal phenotype to an epithelial one. Therefore, HSF1 may be involved in the remodeling of mammary gland architecture over the female lifetime. Moreover, HSF1 levels positively correlated with the invasive phenotype of triple-negative breast cancer cells, and their growth was inhibited by the HSF1 inhibitor DTHIB.