RAS/MAPK activation is associated with reduced Tumor-infiltrating lymphocytes in Triple-Negative Breast Cancer: Therapeutic Cooperation Between MEK and PD-1/PD-L1 Immune Checkpoint Inhibitors

PURPOSE: Tumor-infiltrating lymphocytes (TIL) in the residual disease (RD) of triple-negative breast cancers (TNBC) after neoadjuvant chemotherapy (NAC) are associated with improved survival, but insight into tumor cell-autonomous molecular pathways affecting these features are lacking. EXPERIMENTAL DESIGN: We analyzed TILs in the RD of clinically and molecularly characterized TNBCs after NAC and explored therapeutic strategies targeting combinations of MEK inhibitors with PD-1/PD-L1-targeted immunotherapy in mouse models of breast cancer. RESULTS: Presence of TILs in the RD was significantly associated with improved prognosis. Genetic or transcriptomic alterations in Ras-MAPK signaling were significantly correlated with lower TILs. MEK inhibition upregulated cell surface MHC expression and PD-L1 in TNBC cells both in vivo and in vitro. Moreover, combined MEK and PD-L1/PD-1 inhibition enhanced antitumor immune responses in mouse models of breast cancer. CONCLUSIONS: These data suggest the possibility that Ras-MAPK pathway activation promotes immune-evasion in TNBC, and support clinical trials combining MEK- and PD-L1-targeted therapies. Furthermore, Ras/MAPK activation and MHC expression may be predictive biomarkers of response to immune checkpoint inhibitors

T cell shape is orchestrated by PDZ-containing proteins: Parallels with epithelial polarity

The Cre/loxP system is facilitates excision of DNA sequences located between two loxP sites by the Cre recombinase (Cre) of Bacteriophage P1. Generation of different tissue-specific Cre transgenic mice, which can be used for conditional gene inactivation in specific tissues, is an ideal tool for studying gene function in different tissues in mice. The winged-helix transcription factor, Foxa2, is essential for development of the node and notochord. In mouse, Foxa2 expression is observed in the node, notochord, floor plate and gut epithelium during development. In order to facilitate genetic studies of notochord development, we have used a 520 bp element (mNE) upstream of the Foxa2 gene, which directs specific expression in the node and notochord to generate a mouse line, mNE-Cre, in which the Cre gene was placed under the regulatory control of the mNE and linked to an IRES-lacZ reporter. Staining for b-galactocidase (b-gal) activity revealed that the Cre transgene was expressed from E7.5 to E9.5 specifically in the notochord. Moreover, crossing of the mNE-Cre transgenic mice with the loxP mouse reporter line, Z/EG, resulted in enhanced green fluorescent protein (EGFP) signal specifically in the node and notochord from E8.0 to E9.5. The mNE-Cre mice have been used to conditionally inactivate Smoothened (Smo) in the notochord, and preliminary data revealed that loss of both alleles of Smo in the notochord resulted in embryonic lethality. The mNE-Cre transgenic mice are therefore a useful resource for conditional gene manipulation in the notochord in mice.link_to_subscribed_fulltex

T cell shape and function is orchestrated by a network of T polarity proteins

Loss of polarity is one of the earliest hallmarks of epithelial neoplasia and leads to aberrant communication between the epithelial cell and its microenvironment. Understanding how deregulation of polarity occurs and how it may contribute to tumour formation is a new and unexplored area of cancer research. Genetic screens in Drosophila have identified scribble, discs large (dlg) and lethal giant larvae (lgl) as key epithelial polarity regulators with mutation in any of these genes resulting in loss of polarity, overproliferation and multilayering of epithelial cells leading to 3D-tumourous overgrowth, and in the presence of activated Ras, invasion and metastasis. We have recently described the human homologue of Scribble and demonstrated using complementation studies in Drosophila that expression of human Scribble can also regulate polarity and proliferation. Evidence from cancer patients suggests that Scribble and Dlg could act as a tumour suppressor in some epithelial cancers with, in many cases, low levels of Scribble or Dlg correlating with increased tumour invasiveness and malignancy. We have undertaken a detailed functional analysis of Scribble in mammalian epithelial cells and mice mutant for Scribble and uncovered a critical role for Scribble in the regulation of epithelial polarity required for directed migration during development and wound healing in vivo. In addition, we show that impaired human Scribble can function together with activated Ras to lead to increased invasion and tumourigenesis. Therefore, Scribble can act to promote or inhibit migration dependent on the cellular context. We propose that Scribble and other polarity regulators may be key signalling molecules involved in a new pathway regulating epithelial tumour progression in mammals