RASSF1A disrupts the NOTCH signaling axis via SNURF/RNF4‐mediated ubiquitination of HES1

Abstract

RASSF1A promoter methylation has been correlated with tumor dedifferentiation and aggressive oncogenic behavior. Nevertheless, the underlying mechanism of RASSF1A‐dependent tumor dedifferentiation remains elusive. Here, we show that RASSF1A directly uncouples the NOTCH‐HES1 axis, a key suppressor of differentiation. Interestingly, the crosstalk of RASSF1A with HES1 occurs independently from the signaling route connecting RASSF1A with the Hippo pathway. At the molecular level, we demonstrate that RASSF1A acts as a scaffold essential for the SUMO‐targeted E3 ligase SNURF/RNF4 to target HES1 for degradation. The reciprocal relationship between RASSF1A and HES1 is evident across a wide range of human tumors, highlighting the clinical significance of the identified pathway. We show that HES1 upregulation in a RASSF1A‐depleted environment renders cells non‐responsive to the downstream effects of γ‐secretase inhibitors (GSIs) which restrict signaling at the level of the NOTCH receptor. Taken together, we report a mechanism through which RASSF1A exerts autonomous regulation of the critical Notch effector HES1, thus classifying RASSF1A expression as an integral determinant of the clinical effectiveness of Notch inhibitors.

Epigenetic Regulation in Gastroenteropancreatic Neuroendocrine Tumors

“…For example, the role of genes like RASSF1A that are known to have decreased expression in NETs due to promoter hypermethylation or gene loss, and how these proteins interact with signaling pathways such as Notch. A recent publication demonstrates how loss of RASSF1A expression allows for tumor dedifferentiation and proliferation as a result of accumulated Hes1, suggesting a role for RASSF1A/Notch crosstalk in GEP-NENs that has not yet been explored ( 138 , 139 ). Further, the lysine demethylase protein KDM5A/RBP2, shown to be overexpressed in GEP-NENs ( 107 ), is a key component of the CSL repressor complex in Notch signaling and also may play a role in epigenetic regulation of cancer cell proliferation and stemness.…”

Interplay of Developmental Hippo–Notch Signaling Pathways with the DNA Damage Response in Prostate Cancer

“…A direct connection between the Hippo and Notch signaling pathways in the context of several human cancer types, including prostate, was recently identified, via the tumor suppressor RASSF1A [ 126 ]. RASSF1A is an established activator of the Hippo pathway, which is found epigenetically inactivated in a plethora of tumor types [ 127 ].…”

“…RASSF1A is an established activator of the Hippo pathway, which is found epigenetically inactivated in a plethora of tumor types [ 127 ]. In prostate cancer, RASSF1A has been reported to be silenced in approximately 70% of patient tumors [ 128 ], which correlates with increased levels of the Notch downstream effector HES1 [ 126 ]. This reciprocal correlation between RASSF1A and HES1 was evident in the vast majority of human cancers, implying that the reported RASSF1A–HES1 interplay may be conserved among different tumor types [ 126 ].…”

“…In prostate cancer, RASSF1A has been reported to be silenced in approximately 70% of patient tumors [ 128 ], which correlates with increased levels of the Notch downstream effector HES1 [ 126 ]. This reciprocal correlation between RASSF1A and HES1 was evident in the vast majority of human cancers, implying that the reported RASSF1A–HES1 interplay may be conserved among different tumor types [ 126 ]. Mechanistically, it was demonstrated that RASSF1A stabilizes the E3 ligase RNF4, which targets HES1 for proteasome-dependent degradation, thus preventing the expression of HES1-dependent proliferation and cancer stemness genes [ 126 ].…”

“…This reciprocal correlation between RASSF1A and HES1 was evident in the vast majority of human cancers, implying that the reported RASSF1A–HES1 interplay may be conserved among different tumor types [ 126 ]. Mechanistically, it was demonstrated that RASSF1A stabilizes the E3 ligase RNF4, which targets HES1 for proteasome-dependent degradation, thus preventing the expression of HES1-dependent proliferation and cancer stemness genes [ 126 ]. In contrast, in the absence of RASSF1A, RNF4 reduces its affinity with HES1, which remains stable regardless of upstream Notch signals or the use of Notch inhibitors [ 126 ], indicating that Notch signaling blockade at the receptor level (e.g., with γ-secretase inhibitors) may be fruitful only in the presence of RASSF1A in several cancer types, including prostate.…”