Phosphorylation of MITF by AKT affects its downstream targets and causes TP53-dependent cell senescence

Abstract

Microphthalmia-associated transcription factor (MITF) plays a crucial role in the melanogenesis and proliferation of melanocytes that is dependent on its abundance and modification. Here, we report that epidermal growth factor (EGF) induces senescence and cyclin-dependent kinase inhibitor 1A (CDKN1A) expression that is related to MITF. We found that MITF could bind TP53 to regulate CDKN1A. Furthermore, the interaction between MITF and TP53 is dependent on AKT activity. We found that AKT phosphorylates MITF at S510. Phosphorylated MITF S510 enhances its affinity to TP53 and promotes CDKN1A expression. Meanwhile, the unphosphorylative MITF promotes TYR expression. The levels of p-MITF-S510 are low in 90% human melanoma samples. Thus the level of p-MITF-S510 could be a possible diagnostic marker for melanoma. Our findings reveal a mechanism for regulating MITF functions in response to EGF stimulation and suggest a possible implementation for preventing the over proliferation of melanoma cells.

mTORC1 feedback to AKT modulates lysosomal biogenesis through MiT/TFE regulation

“…and AKT-mediated phosphorylation at S467/S565/S510 both promote cytosolic MiT/TFE retention and/or degradation (15,17,39,40). Though these previous studies focused on the role of AKT in phosphorylation and nuclear translocation of MiT/ TFE proteins, it is notable that we found both total and nuclear levels of MiT/TFEs to be proportionally affected by mTORC1 or AKT modulation.…”

“…Similarly, genetic or longer-term pharmacologic mTORC1 inhibition decreased MiT levels and activity and lysosomal gene transcription. Yet these data are at odds with current models suggesting that mTORC1 suppression pro- S467/S565/S510 in TFEB, TFE3, and MITF, respectively, results in their cytoplasmic retention/inactivation (17,39) or proteasomal degradation (1,40). We conducted a TMT-based phosphoproteomic analysis of control and Rptor-KO keratinocytes, and found p-TFE3 (S564/565) levels to be significantly increased in Rptor-mary neurons showed increased autolysosome formation and autophagic flux via AMPK-dependent ULK1 activation, bypassing mTORC1-dependent ULK1 inhibition (38).…”

“…One consequence of lysosomal/autophagy flux defects, seen in many lysosomal storage diseases, is the accumulation of poly-ubiquitinated proteins (52). Interestingly, AKT activation can increase the ubiquitination and proteasomal degradation of specific substrates (53,54) via phosphorylation, and MiT/TFE proteins are known bonafide proteasomal substrates (55,56) that can be targeted for degradation by phosphorylation via multiple kinases including AKT (40). Additionally, certain ubiquitin ligases involved in MiT/TFE regulation, such as STUB1 (56), are also responsible for the degradation of substrates in a PI3K/AKTdependent manner (54).…”

Pyruvic acid/ethyl pyruvate inhibits melanogenesis in B16F10 melanoma cells through PI3K/AKT, GSK3β, and ROS‐ERK signaling pathways

“…In recent studies, AKT also directly induced MITF phosphorylation at Ser510; p‐MITF is degraded by protease (Wang et al, ). This could explain why the PI3K inhibitor induced more melanin synthesis than the GSK3β inhibitor.…”

MITF—the first 25 years

“…S3, where S409 in MITF-M corresponds to S516 in MITF-A) (Palmieri et al 2017). Using a phosphorylation mimetic "S510D" mutant, Wang et al (2016) reported that MITF was degraded more rapidly, suggesting that AKT promotes MITF degradation. This would be consistent with results from the Ploper et al (2015) study that reported that phosphorylation on S409 primes for phosphorylation by GSK3 at S405, S401, and S397, leading to destabilization of MITF AKT-mediated phosphorylation of MITF was also reported to stimulate MITF interaction with p53 and promote CDKN1A expression, while nonphosphorylated MITF was able to activate better tyrosinase expression .…”