Table 1.
Possible tumorigenicity of HERV-K particles in various organs or tissues, along with tumor risk factors and evidence of HERV-K particles in tumors.
| Tumor Type | Involved Organs or Tissues |
Tumor Risk Factors | Evidence of HERV-K Particles |
|---|---|---|---|
| Melanoma | Skin [70] | Expression/methylation of LINE-1, methylation of HERV-K [75] | HERV-K Gag, Pol, Env, and Rec proteins [76] |
| Teratocarcinoma | mixed germ-line tumors: female sexual gonads, placenta, extraembryonic membranes, and umbilical cord [82,83] | Changing the expression pattern of cytokines and cellular genes due to teratoma-liberated viral proteins [46], deglycosylation of HML-2 GH and Tera-1 [84] | TM 1, HERV-K Env [46] |
| Osteosarcoma | Bones | Dysfunctionality of TE 2 and DNA damages, overexpression of LINE-1/Alu/SVA/HERV-K [85] | Not yet defined |
| Colorectal cancer (CRC) | Colon and rectum | Conversion of NUPR1 into a chromatin protein due to stress condition [86], lower methylation rate of LINE-1 or HERV, EVs 3 [87] | HERV-K Env transcripts class II [88] |
| Breast tumors | Breast [89] | Activation of Ras-dependent ERK 4 1/2 mitogen-activated protein (MAP) kinase pathway and its transformation [90] | HML-2 Env mRNA [38,91], transcripts of Gag and Env genes [91] |
| Ovarian cancer | Ovary [92] | Induction of immunity by HERV-K Env protein and production of T cells, INFγ, and HERV-K-specific CTL 5 [93]. | HERV-K transcripts, Env protein, and active reverse transcriptase [93] |
| Prostate cancer | Prostate [94] | Expression of the NGO-Pr-54 region (a Gag-related antigen) [95], encoding chromosome 22q11.23 by HERV-K Gag proteins [96], overexpression of HERV-K_22q11.23 and accessory Np9 [97], elevated level of interferon-γ and expression of HERV-K Gag [98], chromosomal translocation and amplification, abnormal up-regulation of ETS factors [99], transcriptional activity of HERV-K LTRs [100] | HERV-K Gag and Gag RNA [101], HERV-K Env [98], |
| Atypical teratoid rhabdoid tumors (AT/RT) | Central nervous system (brain) [102] | Deletion of the SMARCB1 gene [103] | HERV-K Env [103] |
| Non-Hodgkin lymphoma (NHL) | Lymphoid tissue [104] | HERV-K expression and its impact in severity or recurrence of NHL [105] | HERV-K DNA, RNA, and proteins [105] |
1 TM: A type of recombinant HERV-K transmembrane envelope. 2 TE: Transposable elements. 3 EVs: Extracellular vesicles. 4 ERK: Extracellular-signal-regulated kinase. 5 CTL: Cytotoxic T lymphocytes.