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Abstract SAMD4 protein family is a class of novel RNA-binding proteins that can mediate post-transcriptional regulation and translation repression in eukaryotes, which are highly conserved from yeast to humans during evolution. In mammalian cells, SAMD4 protein family consists of two members including SAMD4A/Smaug1 and SAMD4B/Smaug2, both of which contain common SAM domain that can specifically bind to different target mRNAs through stem-loop structures, also known as Smaug recognition elements (SREs), and regulate the mRNA stability, degradation and translation. In addition, SAMD4 can form the cytoplasmic mRNA silencing foci and regulate the translation of SRE-containing mRNAs in neurons. SAMD4 also can form the cytosolic membrane-less organelles (MLOs), termed as Smaug1 bodies, and regulate mitochondrial function. Importantly, many studies have identified that SAMD4 family members are involved in various pathological processes including myopathy, bone development, neural development, and cancer occurrence and progression. In this review, we mainly summarize the structural characteristics, biological functions and molecular regulatory mechanisms of SAMD4 protein family members, which will provide a basis for further research and clinical application of SAMD4 protein family.

SAMD4 protein family is a class of novel RNA-binding proteins that can mediate post-transcriptional regulation and translation repression in eukaryotes, which are highly conserved from yeast to humans during evolution. In mammalian cells, SAMD4 protein family consists of two members including SAMD4A/Smaug1 and SAMD4B/Smaug2, both of which contain common SAM domain that can specifically bind to different target mRNAs through stem-loop structures, also known as Smaug recognition elements (SREs), and regulate the mRNA stability, degradation and translation. In addition, SAMD4 can form the cytoplasmic mRNA silencing foci and regulate the translation of SRE-containing mRNAs in neurons. SAMD4 also can form the cytosolic membrane-less organelles (MLOs), termed as Smaug1 bodies, and regulate mitochondrial function. Importantly, many studies have identified that SAMD4 family members are involved in various pathological processes including myopathy, bone development, neural development, and cancer occurrence and progression. In this review, we mainly summarize the structural characteristics, biological functions and molecular regulatory mechanisms of SAMD4 protein family members, which will provide a basis for further research and clinical application of SAMD4 protein family. [ABSTRACT FROM AUTHOR]

Neurons are exceptionally sensitive to oxidative stress, which is the basis for many neurodegenerative disease pathophysiologies. The posttranscriptional basis for neuronal differentiation and behavior is not well characterized. The steady-state levels of mRNA are outcomes of an interplay between RNA transcription and decay. However, the correlation between mRNA transcription, translation, and stability remains elusive. We utilized a SH-SY5Y-based neural differentiation model that is widely used to study neurodegenerative diseases. After neuronal differentiation, we observed enhanced sensitivity of mature neurons to mitochondrial stresses and ferroptosis induction. We employed a newly developed simplified mRNA stability profiling technique to explore the role of mRNA stability in SH-SY5Y neuronal differentiation model. Transcriptome-wide mRNA stability analysis revealed neural-specific RNA stability kinetics. Our analysis revealed that mRNA stability could either exert the buffering effect on gene products or change in the same direction as transcription. Importantly, we observed that changes in mRNA stability corrected over or under transcription of mRNAs to maintain mRNA translation dynamics. Furthermore, we conducted integrative analysis of our mRNA stability data set, and a published CRISPR-i screen focused on neuronal oxidative stress responses. Our analysis unveiled novel neuronal stress response genes that were not evident at the transcriptional or translational levels. SEPHS2 emerged as an important neuronal stress regulator based on this integrative analysis. Motif analysis unveiled SAMD4A as a major regulator of the dynamic changes in mRNA stability observed during differentiation. Knockdown of SAMD4A impaired neuronal differentiation and influenced the response to oxidative stress. Mechanistically, SAMD4A was found to alter the stability of several mRNAs. The novel insights into the interplay between mRNA stability and cellular behaviors provide a foundation for understanding neurodevelopmental processes and neurodegenerative disorders and highlight dynamic mRNA stability as an important layer of gene expression., (© 2024 The Author(s). Journal of Cellular Physiology published by Wiley Periodicals LLC.)

Spermatogenesis is the highly orchestrated process involving expression of a series of testicular genes. Testis-enriched genes are critical for cellular processes during spermatogenesis whose disruption leads to impaired spermatogenesis and male infertility. Nevertheless, among poorly investigated testicular genes are the mouse Samd4a and human SAMD4A which were identified in the current study as novel testis-enriched genes through transcriptomic analyses. In particular, as orthologous alternative splicing isoforms, mouse Samd4a E-form and human SAMD4AC-form containing the SAM domain were specific to testes. Western blot analyses revealed that the murine SAMD4AE-form was predominantly found in the testis. Analyses on GEO2R and single-cell RNA-seq datasets revealed that the Samd4a/SAMD4A expression was enriched in spermatids among various types of cells in adult testes. To investigate in vivo functions of Samd4a, Samd4a knockout mice were generated using the CRISPR/Cas9 system. The Samd4a deficiency resulted in lower testis weight, absence of elongated spermatids, and an increased number of apoptotic cells. Profiling of gene expression in human testis samples revealed that the SAMD4A expression was comparable between obstructive azoospermia patients and normal controls, but significantly lowered in nonobstructive azoospermia (NOA) patients. Among three subgroups of NOA, pre-meiotic arrest (NOA-pre), meiotic arrest (NOA-mei), and post-meiotic arrest (NOA-post), expression level of SAMD4A was higher in the NOA-post than the NOA-mei, but there was no difference between the NOA-pre and NOA-mei. The current studies demonstrated spermatid stage-specific expression of Samd4a/SAMD4A, and impairment of the late stages of spermatogenesis by disruption of the mouse Samd4a gene. These data suggest that Samd4a/SAMD4A plays an essential role in normal spermatogenesis, and SAMD4A, as a spermatid specific marker, can be used for subcategorizing NOA patients. Further understanding the molecular role of SAMD4A will advance our knowledge on genetic regulations in male infertility.

Tumor‐induced angiogenesis is important for further progression of solid tumors. The initiation of tumor angiogenesis is dictated by a shift in the balance between proangiogenic and antiangiogenic gene expression programs. However, the potential mechanism controlling the expression of angiogenesis‐related genes in the tumor cells, especially the process mediated by RNA‐binding protein (RBP) remains unclear. SAMD4A is a conserved RBP across fly to mammals, and is believed to play an important role in controlling gene translation and stability. In this study, we identified the potential role of SAMD4A in modulating angiogenesis‐related gene expression and tumor progression in breast cancer. SAMD4A expression was repressed in breast cancer tissues and cells and low SAMD4A expression in human breast tumor samples was strongly associated with poor survival of patients. Overexpression of SAMD4A inhibited breast tumor angiogenesis and caner progression, whereas knockdown of SAMD4A demonstrated a reversed effect. Mechanistically, SAMD4A was found to specifically destabilize the proangiogenic gene transcripts, including C‐X‐C motif chemokine ligand 5 (CXCL5), endoglin (ENG), interleukin 1β (IL1β), and angiopoietin 1 (ANGPT1), by directly interacting with the stem‐loop structure in the 3′ untranslated region (3′UTR) of these mRNAs through its sterile alpha motif (SAM) domain, resulting in the imbalance of angiogenic genes expression. Collectively, our results suggest that SAMD4A is a novel breast tumor suppressor that inhibits tumor angiogenesis by specifically downregulating the expression of proangiogenic genes, which might be a potential antiangiogenic target for breast cancer therapy. [ABSTRACT FROM AUTHOR]

The incidence and mortality of gastric cancer remain high in the world. We aim to explore the role of SAMD4A in gastric cancer. The expression of SAMD4A was up-regulated in gastric adenocarcinoma and the expression level of SAMD4A in gastric adenocarcinoma and adjacent normal tissues was verified by RT-qPCR. Immunohistochemical showed that SAMD4A was mainly located in the cytoplasm. The result showed that the expression of SAMD4A was positively correlated with the depth of invasion, the number of lymph node metastasis, and the clinical stage in patients with gastric adenocarcinoma. Survival analysis of GEPIA database showed that the overall survival of gastric adenocarcinoma patients with positive SAMD4A expression was lower than that of the negative group. Gastric cancer cell lines with knockdown of the SAMD4A gene were used to observe the differences in cell proliferation, invasion, and migration abilities between the knockdown group and the control group. The results showed that the proliferation, invasion, and migration abilities of the SAMD4A knockdown group were both weakened compared with the control group. This study is the first to find that the expression level of SAMD4A in gastric cancer is higher than that in the adjacent group and is associated with poor prognosis of patients. SAMD4A promotes the proliferation, invasion, and migration of gastric adenocarcinoma cells. This indicates that SAMD4A plays an important role in the occurrence and development of gastric cancer, and is expected to be an effective indicator for the diagnosis and evaluation of the prognosis of gastric cancer. • SAMD4A mRNA expression was significantly higher in gastric cancer than those in the corresponding non-tumorous. • The higher abundance of SAMD4A could predict poor prognosis in gastric cancer patients. • SAMD4A promoted the proliferation of AGS and MKN-45 cells. • SAMD4A promoted the abilities of migration and invasion of AGS and MKN-45 cells. [ABSTRACT FROM AUTHOR]

Spermatogenesis is the highly orchestrated process involving expression of a series of testicular genes. Testis-enriched genes are critical for cellular processes during spermatogenesis whose disruption leads to impaired spermatogenesis and male infertility. Nevertheless, among poorly investigated testicular genes are the mouse Samd4a and human SAMD4A which were identified in the current study as novel testis-enriched genes through transcriptomic analyses. In particular, as orthologous alternative splicing isoforms, mouse Samd4a E-form and human SAMD4A C-form containing the SAM domain were specific to testes. Western blot analyses revealed that the murine SAMD4A E-form was predominantly found in the testis. Analyses on GEO2R and single-cell RNA-seq datasets revealed that the Samd4a / SAMD4A expression was enriched in spermatids among various types of cells in adult testes. To investigate in vivo functions of Samd4a , Samd4a knockout mice were generated using the CRISPR/Cas9 system. The Samd4a deficiency resulted in lower testis weight, absence of elongated spermatids, and an increased number of apoptotic cells. Profiling of gene expression in human testis samples revealed that the SAMD4A expression was comparable between obstructive azoospermia patients and normal controls, but significantly lowered in nonobstructive azoospermia (NOA) patients. Among three subgroups of NOA, pre-meiotic arrest (NOA-pre), meiotic arrest (NOA-mei), and post-meiotic arrest (NOA-post), expression level of SAMD4A was higher in the NOA-post than the NOA-mei, but there was no difference between the NOA-pre and NOA-mei. The current studies demonstrated spermatid stage-specific expression of Samd4a / SAMD4A , and impairment of the late stages of spermatogenesis by disruption of the mouse Samd4a gene. These data suggest that Samd4a / SAMD4A plays an essential role in normal spermatogenesis, and SAMD4A, as a spermatid specific marker, can be used for subcategorizing NOA patients. Further understanding the molecular role of SAMD4A will advance our knowledge on genetic regulations in male infertility., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Ahn, Kim, Park, Suh, Lee, Hwang, Mamuad, Lee and Lee.)