Clinicopathologic significance of nuclear HER4 and phospho-YAP(S¹²⁷) in human breast cancers and matching brain metastases

Abstract

Background: Human epidermal growth factor receptor-4 (HER4) and yes-associated protein-1 (YAP) are candidate therapeutic targets in oncology. YAP’s transcriptional coactivation function is modulated by the HER4 intracellular domain (HER4-ICD) in vitro, but the clinical relevance of this has not been established. This study investigated the potential for targeting the HER4-YAP pathway in brain metastatic breast cancer. Methods: We performed immuno-phenotypic profiling of pathway markers in a consecutive breast cancer series with 25 years of clinical follow up ( n = 371), and patient-matched breast and metastatic brain tumours ( n = 91; 30 pairs). Results: Membrane localisation of phospho-HER4 [pHER4(Y1162)] was infrequent in primary breast cancer, but very frequent in brain metastases (5.9% versus 75% positive), where it was usually co-expressed with pHER3(Y1289) ( p < 0.05). The presence of YAP in tumour cell nuclei was associated directly with nuclear pERK5(T218/Y210) ( p = 0.003). However, relationships with disease-specific survival depended on oestrogen receptor (ER) status. Nuclear pYAP(S127) was associated with smaller, good prognostic ER+ breast tumours (log-rank hazard-ratio 0.53; p = 9.6E−03), but larger, poor prognostic triple-negative cancers (log-rank hazard-ratio 2.78; p = 1.7E−02), particularly when co-expressed with nuclear HER4-ICD ( p = 0.02). This phenotype was associated with stemness and mitotic instability markers (vimentin, SOX9, ID1, SPAG5, TTK, geminin; p < 0.05). YAP expression in brain metastases was higher than matched primary tumours; specifically, nuclear pYAP(S127) in ER-negative cases ( p < 0.05). Nuclear YAP was detected in ~70% of ER-negative, HER4-activated brain metastases. Discussion: Our findings suggest that the canonical-mechanism where Hippo pathway-mediated phosphorylation of YAP ostensibly excludes it from the nucleus is dysfunctional in breast cancer. The data are consistent with pYAP(S127) having independent transcriptional functions, which may include transducing neuregulin signals in brain metastases. Consistent with mechanistic studies implicating it as an ER co-factor, nuclear pYAP(S127) associations with breast cancer clinical outcomes were dependent on ER status. Conclusion: Preclinical studies investigating HER4 and nuclear YAP combination therapy strategies are warranted.

Landscape of Epidermal Growth Factor Receptor Heterodimers in Brain Metastases

“…For example, brain-derived neuregulins (NRG) provide a stimulus for the HER3-PI3K cell survival axis [26][27][28]. This is supported by studies demonstrating increased expression and activation of NRG receptors, HER3 and HER4, in BM compared to matching primary breast and lung tumours [29][30][31][32]. NRG1 has a very strong binding affinity for HER3-HER2 heterodimers [33], and HER3 is an exceptionally strong activator of the PI3K cell survival axis, with six docking sites for PI3K's regulatory substrate p85 [34,35].…”

“…Breast-BM cohort: 41 brain-metastatic breast cancer cases (34 primary breast tumours and 44 BM, of which 28 are 'matched pairs') [31]. HER2 status was extracted from primary breast cancer pathology reports, determined by in situ hybridization (ISH).…”

Targeting HER2 in breast cancer: new drugs and paradigms on the horizon

“…The human epidermal growth factor receptor 2 (HER2) is a tyrosine kinase receptor critically involved in the carcinogenesis of the mammary gland [1]. It is a member of the HER family of tyrosine kinase receptors, including three other members [epidermal growth factor receptor (EGFR), HER3, HER4], widely interconnected into a signaling network with important implications in breast oncogenesis and clinical behavior of breast tumors [2][3][4][5][6]. The study of HER2 oncogenic role and the development of drugs targeting the HER2 receptor have revolutionized breast oncology in the last decades.…”

Characterization of Immune Cell Subsets of Tumor Infiltrating Lymphocytes in Brain Metastases

“…This brain tumor microenvironment (TME) comprises various cell types that can regulate progression of the cancer and also response to therapy [ 5 ]. Given the unique adaptations of the brain TME [ 6 , 7 , 8 , 9 , 10 , 11 ], as well as the presence of uncommon cell types; microglia (MG), neurons, and astrocytes; and, the blood–brain barrier, makes it compelling to further address the critical question of how TME heterogeneity affects therapeutic efficacy.…”