
Figure 1
Early discoveries related to PIWI proteins and piRNA. piRNA, PIWI-interacting RNA; PIWI, P-element induced wimpy testis protein.
Table 1
Important discoveries of PIWI/piRNA expression in various cancers†
| Year | PIWI/piRNA | Expression | Cancer type | Role |
|---|---|---|---|---|
| 2005 | PIWIL2 | Upregulated | Testicular seminoma | Inhibition of apoptosis and promotion of proliferation via Stat3/Bcl-XL signaling pathway [18] |
| 2006 | PIWIL1 | Upregulated | Human gastric cancer | Cell proliferation [19] |
| 2007 | PIWIL1 | Upregulated | Soft tissue sarcoma | Stem cell proliferation [20] |
| 2008 | PIWIL1 | Up/down-regulated | Adenocarcinoma | Poor prognosis and death [21] |
| 2009 | PIWIL1 | Presence in cytoplasm | Esophageal squamous cell carcinoma | Poor prognosis [22] |
| 2010 | PIWIL2 | Varied | Cervical neoplasia | Biomarker [23] |
| 2010 | PIWIL2 | Upregulated | Human breast cancers | Biomarker [24] |
| 2011 | PIWIL1 | Upregulated | Glioma | Tumor progression, poor outcome, and biomarker [25] |
| 2011 | piR-651 | Upregulated | Gastric, colon, lung, and breast cancer | Increases cell proliferation [26] |
| 2011 | PIWIL1 | Upregulated | Colorectal cancer | Leads to poor overall survival, biomarker [27] |
| 2012 | piR-823 | Downregulated | Gastric cancer | Increases cell proliferation [28] |
| 2012 | PIWIL2 | Upregulated | Colon cancer | Metastasis [29] |
| 2013 | PIWI | Upregulated | Stage III epithelial ovarian cancer | Promotes metastasis, biomarker [30] |
| 2013 | piR-932 | Upregulated | Breast cancer | Positive regulator of breast cancer stem cells [31] |
| 2014 | PIWIL1 | Upregulated | Human breast cancer | Cell proliferation [32] |
| 2014 | piRNA-823 | Upregulated | Multiple myeloma | Regulates angiogenesis [33] |
| 2014 | PIWIL1 and PIWIL4 | Varied | Renal cell carcinoma | Related to clinicopathological parameters [34] |
| 2014 | PIWIL1 | Upregulated | Cervical cancer | Promotes chemoresistance [35] |
| 2014 | PIWIL1 | Upregulated | Hepatocellular carcinoma | Reduces proliferation and migration [36] |
| 2015 | piRNA-DQ594040 | Downregulated | Bladder cancer | Promotes cell proliferation, colony formation and functions against apoptosis [37] |
| 2015 | piR-021285 | Upregulated | Breast cancer | Epigenetic remodeling [38] |
| 2015 | PIWIL2 | Upregulated | Prostate cancer | Metastasis [39] |
| 2015 | piR-017061 | Downregulated | Pancreatic cancer | Associated with diseased condition [40] |
| 2015 | piR-015551 | Downregulated | Colorectal cancer | Associated with long ncRNA expression [41] |
| 2015 | PIWIL1 | Downregulated | Chronic myeloid leukemia | Induces growth and metastasis [42] |
| 2015 | PIWIL2 | Upregulated | Cholangiocarcinoma | Involved in shorter survival span and metastasis [43] |
| 2015 | piR-57125 | Downregulated | Renal cell carcinoma | Associated with tumor recurrence and metastasis, prognostic biomarker [44] |
| piR-30924 | Upregulated | |||
| piR-38756 | Upregulated | |||
| 2015 | PIWIL1 | Upregulated | Type 1 endometrial cancer | Tumor progression by downregulating PTEN [45] |
| 2015 | PIWIL2 | Downregulated | Bladder cancer | Related to disease specific and progression free survival [46] |
| 2016 | PIWIL4 | Upregulated | Breast cancer | Metastasis, antiapoptotic activity and proliferation[47] |
| 2016 | FR140858 | Differentially expressed | Head and neck squamous cell carcinoma | Correlated to human papillomavirus infection [48] |
| 2016 | piR-598 | Upregulated | Glioma | Induces growth and proliferation [49] |
| 2017 | PIWIL3 | Upregulated | Melanoma | Induces metastasis [50] |
| 2017 | PIWIL4 | Upregulated | Retinoblastoma | Induces proliferation [51] |
| 2018 | piR-5937 | Varied | Colon cancer | Biomarker [52] |
| piR-28876 | ||||
| 2018 | piR-8041 | Downregulated | Glioblastoma | Related to tumor growth [53] |
| 2018 | PIWIL1 | Upregulated | Gastric cancer | Metastasis [54] |
| 2018 | PIWIL1 and PIWIL2 | Varied | Muscle invasive urothelial bladder cancer | Correlation with clinical factors, biomarkers [55] |
| 2018 | PIWIL4 | Upregulated | Human breast cancer | Cell motility [56] |
| 2019 | piR-823 | Upregulated | Multiple myeloma | Tumor progression [57] |
| 2019 | piR-39980 | Upregulated | Neuroblastoma | Tumor progression and drug resistance [58] |
| 2019 | piR-36712 | Downregulated | Breast cancer | Chemoresistance and tumor progression [59] |
| 2020 | piR-004987 | Upregulated | Lung cancer | Correlated with lung cancer from sputum as compared with normal [60] |
| piR-020809 | Upregulated | |||
| piR-023338 | Downregulated | |||
| piR-011186 | Downregulated | |||
| 2021 | piR-hsa-211106 | Downregulated | Lung cancer | Chemoresistance and tumor progression [61] |
| 2021 | piR-1008 | Upregulated | Lung cancer | |
| piR-28231 | Upregulated | Lung cancer | ||
| piR-11256 | Upregulated | Lung cancer | ||
| piR-30636 | Upregulated | Lung cancer | ||
| piR-24143 | Upregulated | Lung cancer | Biomarker lung cancer [62] | |
| piR-6842 | Upregulated | Lung cancer | ||
| piR-8757 | Upregulated | Lung cancer | ||
| piR-15572 | Upregulated | Lung cancer | ||
| piR-5444 | Upregulated | Lung cancer and serum exosome | ||
| piR-26925 | Upregulated |

Figure 2
Representation of how the present findings for PIWI proteins or piRNA integrate with the emerging hallmarks of cancer in the case of lung cancer. Turquoise represents positively regulated with the hallmark, while red represents negatively regulated with the hallmark. piRNA, PIWI-interacting RNA; P-element induced wimpy testis protein.