TYRP1 mRNA level is stable and MITF-M-independent in drug-naïve, vemurafenib- and trametinib-resistant BRAFV600E melanoma cells

Abstract

TYRP1 mRNA is of interest due to its potential non-coding role as a sponge sequestering tumor-suppressive miRs in melanoma. To our knowledge, there is no report on changes in TYRP1 expression in melanomas after development of resistance to targeted therapies. We used patient-derived drug-naïve RAS Q61R and BRAF V600E melanoma cell lines. In BRAF V600E melanoma cells, resistance to vemurafenib and trametinib was developed. A time-lapse fluorescence microscope was used to rate proliferation, qRT-PCR and Western blotting were used to assess TYRP1 expression and MITF-M level and activity. A high TYRP1 protein level in RAS Q61R cells corresponded with high TYRP1 mRNA level, whereas undetectable TYRP1 protein in BRAF V600E cells was accompanied by medium mRNA level, also in cells carrying NF1 R135W variant in addition. TYRP1 expression was MITF-M-independent, since similar transcript status was found in MITF-M high and MITF-M low cells. For the first time, we showed that TYRP1 expression remained unaltered in melanoma cells that became resistant to vemurafenib or trametinib, including those cells losing MITF-M. Also drug discontinuation in resistant cells did not substantially affect TYRP1 expression. To verify in vitro results, publicly available microarray data were analyzed. TYRP1 transcript levels stay unaltered in the majority of paired melanoma samples from patients before treatment and after relapse caused by resistance to targeted therapies. As TYRP1 mRNA level remains unaltered in melanoma cells during development of resistance to vemurafenib or trametinib, therapies developed to terminate a sponge activity of TYRP1 transcript may be extended to patients that relapse with resistant disease.

Fluorescence biomarkers of malignant melanoma detectable in urine

“…We determined increasing expression of HIF-1α with increasing malignancy (relative gene expression for pT1ab was 2.18 times higher than for the controls, pT2ab was 1.89 times higher, pT3ab was 3.60 times higher, pT4ab was 3.96 times higher, undefined pT stage was 2.91 times higher). The same tendency was observed by other groups [61][62][63][64].…”

Role of miRNAs in Melanoma Metastasis

“…A large number of non-canonical binding sites for miRNAs have been identified in mRNAs, and several mRNAs are considered sponges that sequester tumour-suppressive miRNAs [44]. These aberrant miRNA–RNA interactions can contribute to the development of melanoma [45] and may be preserved in drug-resistant melanoma cells [46].…”

17-Aminogeldanamycin Inhibits Constitutive Nuclear Factor-Kappa B (NF-κB) Activity in Patient-Derived Melanoma Cell Lines

“…We did not choose BCL2A1, although its basal expression was highly upregulated in DMBC21 compared with DMBC11 cells, as BCL2A1 is also a target of microphthalmia-associated transcription factor (MITF), which is a melanoma-specific protein [28]. In agreement, we have previously demonstrated substantial upregulation of BCL2A1 expression in MITF high melanoma cells [29][30][31][32]. We assessed mRNA levels of selected genes in six melanoma cell lines assigned to the BRAF V600E or NRAS Q61R subtype.…”