Mitochondrial Ribosomal Proteins: History
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Mammalian mitochondrial ribosomes translate 13 proteins encoded by mitochondrial genes, all of which play roles in the mitochondrial respiratory chain. After a long period of reconstruction, mitochondrial ribosomes are the most protein-rich ribosomes. Mitochondrial ribosomal proteins (MRPs) are encoded by nuclear genes, synthesized in the cytoplasm and then, transported to the mitochondria to be assembled into mitochondrial ribosomes. MRPs not only play a role in mitochondrial oxidative phosphorylation (OXPHOS). Moreover, they participate in the regulation of cell state as apoptosis inducing factors. Abnormal expressions of MRPs will lead to mitochondrial metabolism disorder, cell dysfunction, etc. Many researches have demonstrated the abnormal expression of MRPs in various tumors.

  • Mitochondrial Ribosomal Proteins
  • Ribosome
  • tumor

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1. Introduction

Ribosome is the ribonucleoprotein particle, which is an organelle for protein synthesis in cells, and its function is to synthesize the polypeptide chain efficiently and accurately according to the information of mRNA. Ribosomes can be found in almost all cells and even the smallest and simplest mycoplasma cell contains hundreds of them. At present, only mammalian mature red blood cells have no ribosomes, therefore, ribosomes are an indispensable structure of most cells. Mitochondria and chloroplasts contain ribosomes that synthesize their own proteins, which may be related to the origin of mitochondria and chloroplasts. The accepted endosymbiotic origin theory holds that mitochondria and chloroplasts originated from symbiotic bacteria and cyanobacteria in primitive eukaryotic, respectively. Therefore, mitochondrial ribosomes are more similar to the bacterial ribosomes than to cytoplasmic ribosomes. Mitochondrial ribosomal proteins (MRPs) are encoded by nuclear genes and synthesized by the cytoplasm 80S ribosomes, after specific targeting, sorting, transporting to mitochondria, and then assembling into mitochondrial ribosome small and large subunits with two rRNAs encoded by mitochondrial DNA (mt-DNA).

2. MRPs Associated with Diseases

With the research on MRPs, their names have changed [1], as shown in Table 1. The table also shows the changes of MRPs in tumor tissues reported in the past 5 years.

Table 1. Summary of the relationship between abnormal expression of mitochondrial ribosomal proteins and their encoding genes with diseases in recent 5 years.

Old Name New Name Cancer Other Diseases
Mitochondrial ribosomal large subunit (mt-LSU) genes and proteins.
MRPL1 uL1m Lung cancer [2]  
MRPL3 uL3m   Neurodegeneration and memory impairment [3], Hypertrophic cardiomyopathy [4,5], Prognosis [6], Acute mountain disease [7]
MRPL9 bL9m Breast cancer [8]  
MRPL10 uL10m   Early age-related macular degeneration [9]
MRPL11 uL11m   Mitochondrial encephalopathy [10] ↓
MRPL12/L7 bL12m Breast cancer [11] ↑, Colorectal cancer [12]  
MRPL13 uL13m Liver cancer [13] ↓, Breast cancer [13,14,15] ↑  
MRPL15 uL15m Breast cancer [16] ↑  
MRPL16 uL16m   Septic cardiomyopathy [17] ↑
MRPL17 bL17m Lung cancer [18] ↑  
MRPL19 bL19m Endometrial cancers [19,20], Diffuse non-Hodgkin lymphoma [21], Melanoma [22]  
MRPL21 bL21m Acute myeloid leukemia [23] ↑  
MRPL23 uL23m Oral squamous cell carcinoma [24] ↓, Glioblastoma multiforme [25]  
MRPL24 uL24m   Cerebellar atrophy, intellectual disability [26] ↓
MRPL28 bL28m Gastric cancer [27]  
MRPL33 bL33m Breast cancer [28] ↑, Lung cancer, colon cancer [29] ↑, Gastric cancer [30], Acute myeloid leukemia and neuroblastoma [31] ↑, Human papillomavirus associated oropharyngeal squamous cell carcinoma [32] ↑  
MRPL34 bL34m   Cardiomyocyte hypertrophy [33] ↓
MRPL35 bL35m Glioblastoma multiforme [34] ↑, Colorectal cancer [35] ↑  
MRPL36 bL36m   Cri-du-chat syndrome [36]
MRPL37 mL37   Venous thromboembolism [37]
MRPL38 mL38 Liver cancer [38]  
MRPL39 mL39 Gastric cancer [39] ↓  
MRPL40 mL40   Schizophrenia [40,41,42] ↓
MRPL42 mL42 Glioma [43] ↑  
MRPL43 mL43 Gastric cancer [44] ↑  
MRPL44 mL44   Mitochondrial encephalopathy [10] ↓, Cardiomyopathy [45,46]. Hemiplegia migraine, pigmentary retinopathy, renal insufficiency, Leigh-like lesions on brain MRI [47], Asthma and allergy-related traits [48]
MRPL46 mL46 Ovarian cancer [49]  
MRPL47 mL47 Acute lymphoblastic leukemia [50]  
MRPL50 mL50   Cardiomyocyte hypertrophy [33] ↑
MRPL51 mL51 Lung cancer [51] ↑  
MRPL52 mL52 Colorectal cancer [52] ↓  
MRPL54 mL54 Breast cancer [53]  
CRIF1 mL64 Hepatocellular carcinoma [54] ↓, T-cell leukemia [55] Acute radiation syndrome [56], Endothelial inflammation [57,58] ↓, Autoimmune arthritis [59] ↑
MRPS18-A mL66 Liver cancer [60] ↑, Cholangiocarcinoma [61] ↑  
Mitochondrial ribosomal small subunit (mt-SSU) genes and proteins
MRPS2 uS2m Glioblastoma multiforme [25] Cardiomyocyte hypertrophy [33] ↑
MRPS5 uS5m   Noise-induced hearing loss and anxiety related behavior changes [62] ↑
MRPS7 uS7m Osteosarcoma [63] ↑ Primary hypogonadism, primary adrenal failure [64] ↓
MRPS11 uS11m Uveal melanoma [65] ↑  
MRPS12 uS12m Glioblastoma multiforme [25]  
MRPS14 uS14m   Perinatal hypertrophic cardiomyopathy [66] ↑
MRPS18-B mS40 Prostate cancer [67] ↑, Colorectal carcinoma [68] Tuberculosis [69]
MRPS18-C bS18m Breast cancer [70] ↑ Epileptic encephalopathy [71]
MRPS21 bS21m   Cardiomyocyte hypertrophy [33] ↑
MRPS22 mS22   Epicanthus inversus syndrome [72], Hypertrophic cardiomyopathy and fallopian tube lesions [73] ↓, Primary ovarian insufficiency [74,75,76]
MRPS23 mS23 Hepatocellular carcinoma [77] ↑  
MRPS34 mS34 Glioblastoma multiforme [25] Cardiomyocyte hypertrophy [33] ↓
MRPS37 mS37 Acute lymphoblastic leukemia [23] ↑  
MRPS39 mS39   Leigh syndrome [78]

Legend: Prefix “u”: Genes and proteins are present in all kingdoms of life (for universal); prefix “u”: Genes and proteins are bacterial in origin and do not have an eukaryotic (or archaeal) homolog; prefix “m”: Genes and proteins are mitochondrion-specific. “↑” Upregulation in that disease; “↓” downregulation in that disease. This table only lists the MRPs (mitochondrial ribosomal proteins) that appear in this article.

 

 

 

3. Conclusions and Perspectives

The development of a high-precision analysis technology of cryo-electron microscopy enables us to identify the structure of mitochondrial ribosomal proteins with a scale of 0.1 nm. Each of the 80 MRPs is essential for the mitochondrial ribosome composition, which plays an irreplaceable role in the assembly and translation of mitochondrial DNA. At present, studies of the relationship between MRPs and cell apoptosis are few. Although the apoptotic mechanisms of MRPS29, MRPL41 and MRPL65 have not been fully elucidated, they at least provide us with useful information to deeply study the apoptotic mechanisms of MRPs. We can further explore the changes of MRPs function or pathway-activating role in the process of inducing apoptosis, based on the analysis of the MRPs structure. Additionally, specific mechanisms can be clarified in the future.

The abnormal expression of MRPs and their encoding genes is closely associated with a variety of cancer and mitochondrial related diseases. Multiple MRPs are important predictors of disease diagnosis. However, the specific mechanisms of inducing the development of diseases is little known.

In the future, on the one hand, it is very important to strengthen the research on the relationship between the abnormal expression of MRPs, lack of their encoding genes, and diseases. On the other hand, some MRPs such as MRPS22, MRPL44 and MRPL28 that have been clarified as key factors in the development of cancer, which can be as biological targets to deeply study their specific pathways of influence, in order to lay a theoretical foundation for a targeted diagnosis and therapy of cancer in our research.

This entry is adapted from the peer-reviewed paper 10.3390/ijms21228879

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