Differential phosphorylation of two serine clusters in mouse HORMAD1 during meiotic prophase I progression.

Mouse HORMAD1 is a phospho-protein involved in multiple functions during meiotic prophase I. To obtain insight into the significance of its phosphorylation, we generated phospho-specific antibodies against two serine residues, Ser307 and Ser378, representing each of two serine clusters in mouse HORMAD1. The Ser307 phosphorylation is detectable from early leptotene substage in both wild-type and Spo11-/- spermatocytes, indicating that Ser307 is a primary and SPO11-independent phosphorylation site. In contrast, the Ser378 phosphorylation is negligible at earlier substages in wild-type and Spo11-/- spermatocytes. After mid-zygotene substage, the Ser378 phosphorylation is abundant on unsynapsed chromosome axes in wild-type spermatocytes and is detected only in a part of unsynapsed chromosome axes in Spo11-/- spermatocytes. We also generated a non-phosphorylated Ser307-specific antibody and found that Ser307 is phosphorylated on sex chromosome axes but is almost entirely unphosphorylated on desynapsed chromosome axes in diplotene spermatocytes. These results demonstrated a substage-specific phosphorylation status of mouse HORMAD1, which might be associated with multiple substage-specific functions.

The cancer testes antigen, HORMAD1, limits genomic instability in cancer cells by protecting stalled replication forks.

Tumors anomalously induce the expression of meiotic genes, which are otherwise restricted only to developing gametes. If and how these aberrantly expressed meiotic proteins influence DNA metabolism is not clear, but could have important implications for how tumors acquire and mitigate genomic instability. HORMAD1 is a highly conserved meiotic protein that is frequently expressed in lung adenocarincoma where its expression correlates with reduced patient survival and increased mutation burden. Here, we find that HORMAD1 associates with the replisome and is critical for protecting stalled DNA replication forks. Loss of HORMAD1 leads to nascent DNA strand degradation, an event which is mediated by the MRE11-DNA2-BLM pathway. We find that these phenotypes are due to limited RAD51 loading onto stalled replication forks in the absence of HORMAD1. Ultimately, loss of HORMAD1 leads to increased DNA breaks and chromosomal defects, which is exacerbated dramatically by induction of replication stress. Tumor cells proliferate despite encountering chronic replication stress, placing them on the precipice of catastrophic genomic damage. Our data support the hypothesis that the aberrant expression of HORMAD1 is engaged to attenuate the accumulation of excessive DNA damage due to chronic replication stress, which may otherwise lead to accumulation of toxic levels of genomic instability.

HORMAD1 overexpression predicts response to anthracycline-cyclophosphamide and survival in triple-negative breast cancers.

Triple negative breast cancers (TNBCs) represent 15-20% of all breast cancers and are associated with higher recurrence and distant metastasis rate. Standard of care for early stage TNBC is anthracyclines combined with cyclophosphamide (AC) followed by taxanes, in the neo-adjuvant or adjuvant setting. This work aimed to identify predictive biomarkers of AC response in patient-derived xenograft (PDX) models of TNBC and to validate them in the clinical setting. By gene and protein expression analysis of 39 PDX with different responses to AC, we found that high expression of HORMAD1 was associated with better response to AC. Both gene and protein expression were associated with promoter hypomethylation. In a cohort of 526 breast cancer patients, HORMAD1 was overexpressed in 71% of TNBC. In a second cohort of 186 TNBC patients treated with AC, HORMAD1 expression was associated with longer metastasis-free survival (MFS). In summary, HORMAD1 overexpression was predictive of an improved response to AC in PDX and is an independent prognostic factor in TNBC patients treated with AC.

Structural and biochemical insights into the interaction mechanism underlying HORMAD1 and its partner proteins.

The mammalian HORMA domain-containing protein 1 (HORMAD1) regulates DNA mismatch repair and homologous recombination (HR) repair in many cancers. Here, we show that the structure of human HORMAD1 adopts a self-closed conformation and displays an intra-molecular HORMA domain-closure motif interaction mode. Structural and biochemical data suggest that the interaction modes of the peptide motifs from HORMAD2 and MCM9 with HORMAD1 are highly similar to that of HORMAD1 own closure motif. The peptide motifs from diverse binding partners of HORMAD1 share a conserved Ser-Glu-Pro sequence. Additionally, structural comparison unveiled the HORMA-peptide motif interaction mode diversity among HORMA-containing proteins. Finally, cell-based assays revealed that this HORMA-closure motif interaction pattern contributes to DNA mismatch repair and is required for HORMAD1-dependent HR repair. Together, our results provide structural and biochemical insights into the common theme and functional plasticity of the HORMA domain-containing protein family, and also reveal a universal regulation mechanism for HORMAD1.

The cancer/testis antigen HORMAD1 promotes gastric cancer progression by activating the NF-κB signaling pathway and inducing epithelial-mesenchymal transition.

OBJECTIVES: HORMAD1 is a cancer/testis antigen (CTAs) that regulates DNA homologous recombination, mismatch repair, and other tumor characteristics. However, its role and regulatory mechanisms in gastric cancer remain unclear. METHODS: We performed transcriptomic profiling on seven gastric cancers and paired tissues; HORMAD1 was significantly upregulated in gastric cancer samples and was related to poor prognosis survival. Furthermore, cancer pathway microarray, bioinformatic analysis, western blot, and immunochemistry assay demonstrated that HORMAD1 affected the NF-κB signaling pathway. RESULTS: In vitro and vivo studies confirmed that HORMAD1 knockdown inhibited cell growth and invasion, whereas overexpression reversed these effects. Mechanistically, HORMAD1 regulates the epithelial-mesenchymal transition process (EMT) via the NF-κB pathway by increasing the phosphorylation levels of NF-κB (p-65) and Iκκ-ß. Downstream target genes of the NF-κB signaling pathway, such as c-Myc, CyclinD1, may be involved in HORMAD1-induced tumorigenesis in gastric cancer (GC). CONCLUSIONS: HORMAD1 plays an important role in gastric cancer progression and could be a promising prognostic biomarker and therapeutic target.

Ectopically Expressed Meiosis-Specific Cancer Testis Antigen HORMAD1 Promotes Genomic Instability in Squamous Cell Carcinomas.

Genomic instability is a prominent hallmark of cancer, however the mechanisms that drive and sustain this process remain elusive. Research demonstrates that numerous cancers with increased levels of genomic instability ectopically express meiosis-specific genes and undergo meiomitosis, the clash of mitotic and meiotic processes. These meiotic genes may represent novel therapeutic targets for the treatment of cancer. We studied the relationship between the expression of the meiosis protein HORMAD1 and genomic instability in squamous cell carcinomas (SCCs). First, we assessed markers of DNA damage and genomic instability following knockdown and overexpression of HORMAD1 in different cell lines representing SCCs and epithelial cancers. shRNA-mediated depletion of HORMAD1 expression resulted in increased genomic instability, DNA damage, increased sensitivity to etoposide, and decreased expression of DNA damage response/repair genes. Conversely, overexpression of HORMAD1 exhibited protective effects leading to decreased DNA damage, enhanced survival and decreased sensitivity to etoposide. Furthermore, we identified a meiotic molecular pathway that regulates HORMAD1 expression by targeting the upstream meiosis transcription factor STRA8. Our results highlight a specific relationship between HORMAD1 and genomic instability in SCCs, suggesting that selectively inhibiting HORMAD1, possibly, through STRA8 signaling, may provide a new paradigm of treatment options for HORMAD1-expressing SCCs.

Transcriptomic analyses identify key differentially expressed genes and clinical outcomes between triple-negative and non-triple-negative breast cancer.

PURPOSE: There are significant differences in the biological behavior between triple-negative breast cancer (TNBC) and non-triple-negative breast cancer (non-TNBC). In the present study, we identify key differential genes and clinical outcomes between TNBC and non-TNBC. MATERIALS AND METHODS: Transcriptomic analyses used GEO datasets (GSE76275), gene ontology, KEGG pathway analysis and cBioPortal. Quantitative RT-PCR analysis (qRT-PCR) was used to validate the differentially expressed genes. We used the KM Plotter Online Tool and 240 patients with TNBC tissue microarray to assay the prognostic value of HORMAD1. RESULTS: The upregulated differentially expressed genes were enriched in transcription factor activity, sequence-specific DNA binding and nucleic acid binding transcription factor activity. Only 16 genes were upregulated when further screened for fold change >4-fold change. HORMAD1 and SOX8 exhibited high frequencies of change of greater than 10% (HORMAD1 was close to 20%). qRT-PCR results indicated that HORMAD1 and SOX8 mRNA levels were significantly upregulated in TNBC samples. In KM Plotter Online Tool, high HORMAD1 was associated with worse outcome. In our tissue microarray (including 240 TNBC tissues), IHC analysis revealed that 29.7% (55/240) of the tumor samples exhibited high HORMAD1 expression and 70.3% (185/240) of the tumor samples exhibited low HORMAD1 expression levels. Meanwhile, high HORMAD1 group has a bad prognosis. CONCLUSION: The status of transcriptional activation is an important difference between TNBC and non-TNBC. HORMAD1 is a key differential gene associated with poor outcome in TNBC. Epigenetic therapy and agents targeting cancer/testis antigens might potentially help to customize therapies of TNBC.

Epigenetic activation of HORMAD1 in basal-like breast cancer: role in Rucaparib sensitivity.

Basal-like breast cancer (BLBC) is an aggressive breast cancer subtype with features similar to the basal cells surrounding the mammary ducts. Treatment of patients with BLBC has been challenging due to the lack of well-defined molecular targets. Due to the clinical and pathological similarities of BLBC with BRCA-deficient breast cancers, the effectiveness of Poly (ADP-ribose) polymerase inhibitors (PARPi) has been tested in early phase clinical trials for patients with advanced BLBC, with limited clinical responses. Recently, it was reported that HORMAD1 overexpression sensitizes BLBC to HR-targeting agents by suppressing homologous recombination. Our independent analysis suggests that HORMAD1 is aberrantly overexpressed in about 80% of BLBC, and its expression in normal tissues is restricted to testis. Our experimental data suggests that HORMAD1 overexpression correlates with focal hypomethylation in BLBC. On the other hand, investigation of the Genomics of Drug Sensitivity in Cancer dataset revealed significantly reduced sensitivity of HORMAD1-overexpressing BLBC cell lines to Rucaparib, a commonly used PARPi. To further assess the role of HORMAD1 in PARPi sensitivity, we generated three HORMAD1-overexpressing xenograft models using the HORMAD1-low BLBC cell lines HCC1954, HCC1806, and BT20; we then subjected these xenograft models to Rucaparib treatment. Ectopic expression of HORMAD1 enhances tumor formations in two of these models, and significantly reduces sensitivity to Rucaparib in the HCC1954 model. Taken together, our data suggest that epigenetic activation of HORMAD1 by hypomethylation in BLBC may endow reduced sensitivity to Rucaparib treatment in some tumor models.

Repair of exogenous DNA double-strand breaks promotes chromosome synapsis in SPO11-mutant mouse meiocytes, and is altered in the absence of HORMAD1.

Repair of SPO11-dependent DNA double-strand breaks (DSBs) via homologous recombination (HR) is essential for stable homologous chromosome pairing and synapsis during meiotic prophase. Here, we induced radiation-induced DSBs to study meiotic recombination and homologous chromosome pairing in mouse meiocytes in the absence of SPO11 activity (Spo11YF/YF model), and in the absence of both SPO11 and HORMAD1 (Spo11/Hormad1 dko). Within 30 min after 5 Gy irradiation of Spo11YF/YF mice, 140-160 DSB repair foci were detected, which specifically localized to the synaptonemal complex axes. Repair of radiation-induced DSBs was incomplete in Spo11YF/YF compared to Spo11+/YF meiocytes. Still, repair of exogenous DSBs promoted partial recovery of chromosome pairing and synapsis in Spo11YF/YF meiocytes. This indicates that at least part of the exogenous DSBs can be processed in an interhomolog recombination repair pathway. Interestingly, in a seperate experiment, using 3 Gy of irradiation, we observed that Spo11/Hormad1 dko spermatocytes contained fewer remaining DSB repair foci at 48 h after irradiation compared to irradiated Spo11 knockout spermatocytes. Together, these results show that recruitment of exogenous DSBs to the synaptonemal complex, in conjunction with repair of exogenous DSBs via the homologous chromosome, contributes to homology recognition. In addition, the data suggest a role for HORMAD1 in DNA repair pathway choice in mouse meiocytes.

Putative immunogenicity expression profiling using human pluripotent stem cells and derivatives.

Autologous human induced pluripotent stem cells (hiPSCs) should allow cellular therapeutics without an associated immune response. This concept has been controversial since the original report that syngeneic mouse iPSCs elicited an immune response after transplantation. However, an investigative analysis of any potential acute immune responses in hiPSCs and their derivatives has yet to be conducted. In the present study, we used correlative gene expression analysis of two putative mouse "immunogenicity" genes, ZG16 and HORMAD1, to assay their human homologous expression levels in human pluripotent stem cells and their derivatives. We found that ZG16 expression is heterogeneous across multiple human embryonic stem cell and hiPSC-derived cell types. Additionally, ectopic expression of ZG16 in antigen-presenting cells is insufficient to trigger a detectable response in a peripheral blood mononuclear cell coculture assay. Neither of the previous immunogenicity-associated genes in the mouse currently appears to be relevant in a human context.

Failure of homologous synapsis and sex-specific reproduction problems.

The prophase of meiosis I ensures the correct segregation of chromosomes to each daughter cell. This includes the pairing, synapsis, and recombination of homologous chromosomes. A subset of chromosomal abnormalities, including translocation and inversion, disturbs these processes, resulting in the failure to complete synapsis. This activates the meiotic pachytene checkpoint, and the gametes are fated to undergo cell cycle arrest and subsequent apoptosis. Spermatogenic cells appear to be more vulnerable to the pachytene checkpoint, and male carriers of chromosomal abnormalities are more susceptible to infertility. In contrast, oocytes tend to bypass the checkpoint and instead generate other problems, such as chromosome imbalance that often leads to recurrent pregnancy loss in female carriers. Recent advances in genetic manipulation technologies have increased our knowledge about the pachytene checkpoint and surveillance systems that detect chromosomal synapsis. This review focuses on the consequences of synapsis failure in humans and provides an overview of the mechanisms involved. We also discuss the sexual dimorphism of the involved pathways that leads to the differences in reproductive outcomes between males and females.