Table 2 Post-translational modification, and other molecular events involved in tumor reversion

Retinoblastoma (RB)

RB1

Phosphorylation

Breast Cancer (MCF-7)

Axolotl Oocyte Extracts (AOE)

pRB and it’s nuclear localization reduced upon extract treatment, but not of CDKN1B (p27) in early hrs (6 h), but increased 12 h post-treatment. During reprogramming, induction of cell cycle arrest occurs during the process in oocyte extracts and it is stably maintained in treated tumor xenografts, and reprogrammed tumors showed reduced phosphorylation of RB at S780.

Saad et al 2018, [101]

CDKN1B

p27

Phosphorylation

MDA-MB-468 and MDA-MB-231 (Human breast cancer lines), and murine NIH/3T3 cells.

GGTI-2418

In normal cells, p27 inhibits nuclear Cdk activities and is thus considered a tumor suppressor. p27 expression is essential for tumor reversion. Phosphorylation at pY74 & pY88 of p27 activates p27 bound Cdk2/cyclin E complexes, which in turn transform p27 from an inhibitor of Cdk2 inhibitor to a Cdk2 substrate and eventually increases p27 expression.

Kazi et al 2009, [102]

GATA binding protein 1

GATA1

Phosphorylation and Acetylation

Cos 7 and NIH/3T3 Cells.

Tylase Inhibitor Trichostat in A (TSA).

Effect of different agents was tested on GATA-1 modifications in COS7 and NIH/3T3 cell line. Both SCF and erythropoietin elevated phosphorylation of GATA-1. The mutations in the phospho-site abrogated the phosphorylation shifts and protein turnover. Consistent with the idea that both acetylation and phosphorylation are required for turnover. The acetylation mutants were observed to be stable under mitogen stimulatory conditions and, moreover, that mitogen stimulation preferentially leads to the degradation of acetylated GATA-1.

Hernandez et al 2006, [103]

Protein kinase D1

PRKD1

DNA methylation

Breast Cancer cell lines (MDA-MB-231).

Bisulfite Sequencing

Inhibition of methylation of the PRKD1 promoter with DNA methyltransferase inhibitors can lead to re-expression of PKD1 and reversion of the invasive phenotype

Borges et al 2013, [104]

Glutathione S-transferase P1

GSTP1

Methylation

LNCaP human PCA cells

Procainamide

LNCaP PCA cells expressing GSTP1 appeared only after decreased GSTP1 promoter methylation (antagonistic to gene expression) after prolonged 5-aza-C exposure (for many generations), 5-aza-Ctreated LNCaP PCA cells that had unmethylated GSTP1 promoter expressing GSTP1 mRNA as well as the corresponding polypeptides, regardless whether or not 5-aza-C present in the growth medium.

Lin et al 2001 [105]

RARB, CST6, CDKN2A and CCND2

RARB, CST6, CDKN 2A and CCND 2

Demethylation

MCF-7 & HCC1954 cell lines

Amphibian Oocyte Extracts ( AOE).

AOE induced higher demethylation levels for RARB and CST6 promoters than AOE, but CDKN2A and CCND2 showed similar levels of demethylation by either extract. Interestingly, embryonic stem cells extract (ESCE) can slightly induce RARB and CDKN2A demethylation, which is consistent with the inability of this extract to re-activate their expression. Demethylation of CGs from 8 to 13 was found for RARB, CGs 1–8, 14–18, 25 and 31 for CST6, CGs 1–7, and 21–28 for CCND2, and CGs 1–9 and 19–28 for CDKN2A.

Allegrucci et al 2011 [106]

Glycodelin (Progestagen Associated Endometrial Protein, PAEP or Placental Protein 14)

PP14

Deglycosylation

HEC-1B cells (ATCC HTB-113)

Glycodelin Isoform, Glycodelin-A (GdA)

Using enzymatic deglycosylation and/or differentially glycosylated glycodelin isoforms, it was observed that GdA help proliferating PBMC, trophoblast invasion was glycosylation dependent. Regardless of the differences in glycosylation between GdA and HEC-1B, both of them inhibited trophoblast invasion in a comparable potency.

Hautala et al 2020, [107]

Sialidase

NEU1

Murine melanoma variant B16-BL6 (B16 murine melanoma)

Lysosomal Sialidase

Sialidase impact was studied by using i.v. in syngeneic C57BL/6 mice, as well as in cell lines. In cell line, a reduction in metastasis from 40 to 76% was observed in the sialidase transfectants. The metastatic nodules in the transfectants reduced in comparison to the control. Reduced lung metastasis was seen in athymic BALB/c nude, and SCID mice suggested the role of immune system in weakling of the metastasis.

Kato et al 2001, [108]

Focal adhesion kinase 1

FAK

Phosphorylation

Lewis Lung Carcinoma cells (LLC)

FAKY861

Vessel regression can be determined and the study used the mouse model and concluded that the pY861 site phosphorylation is crucial in blood vessel regression in the tumor phenotype in Pdgfr b Cre+; FAKY861F/Y861F mice.

Lees et al 2020 [109]

Tumor Protein TP53

P53

DNA methylation

K7M2 and K12 (murine osteosarcoma) cell populations with differing metastatic potentials (K7M2 is highly metastatic to the lung but K12 is less metastatic)

Chick Embryo Extract (CEE)

CEE extract able to revert the DNA methylation p16, TP53, and ECAD genes. Further, these results were corroborated by the PCR assay as mRNA upregulation was observed post-CEE treatment. The demethylation induced by CEE promotes expression of the above-mentioned genes, and led to reversion of the metastatic phenotypes in highly metastatic osteosarcoma cells.

Mu et al 2014 [110]

Ganglioside Monosialic 2 / Ganglioside Monosialic 3

GM2/G M3

Silylation / Phosphorylation

Bladder cancer cells

Anti-GD2 monoclonal Antibodies

GM3 or GM2 gangliosides induced reversion from oncogenic to normal phenotypes via formation of a complex of tetraspanin CD9 or CD82 in the microdomains. Once GM3/CD9/integrin α3 complex formed in Bladder cells, tumor cells’s phenotype suppressed. GM2 and CD82 together inhibits tyrosine kinase activity upon interaction with MET. Also the cross talk between integrin with Met33. Gangliosides with high levels of silylated. Gangliosides control integrin α5β1-mediated epithelial cells adhesion to FN (fibronectin) via carbohydrate-carbohydrate interactions.

Tsuchida et al 2018 [111], Furukawa et al 2012 [112]

Cyclin-Dependent Kinase Inhibitor 2A (CDKN2A)

CDKN2A or P16

Demethylation

Different tumor types including gastric, colonic, ovarian, breast, renal, lung cancer & melanoma.

DNMT1 Inhibitor (MG98)

MG98 is an anti-sense oligonucleotide binds to 3′-UTR of DNMT1 in human cells, and that results in demethylation of selected genes by reducing the CpG island and allowing the tumor suppressor genes to re-express.

Plummer et al 2009 [113]