RNA‐Binding Protein L1TD1 Interacts with LIN28 via RNA and is Required for Human Embryonic Stem Cell Self‐Renewal and Cancer Cell Proliferation

Abstract

Human embryonic stem cells (hESC) have a unique capacity to self-renew and differentiate into all the cell types found in human body. Although the transcriptional regulators of pluripotency are well studied, the role of cytoplasmic regulators is still poorly characterized. Here, we report a new stem cell-specific RNA-binding protein L1TD1 (ECAT11, FLJ10884) required for hESC self-renewal and cancer cell proliferation. Depletion of L1TD1 results in immediate downregulation of OCT4 and NANOG. Furthermore, we demonstrate that OCT4, SOX2, and NANOG all bind to the promoter of L1TD1. Moreover, L1TD1 is highly expressed in seminomas, and depletion of L1TD1 in these cancer cells influences self-renewal and proliferation. We show that L1TD1 colocalizes and interacts with LIN28 via RNA and directly with RNA helicase A (RHA). LIN28 has been reported to regulate translation of OCT4 in complex with RHA. Thus, we hypothesize that L1TD1 is part of the L1TD1-RHA-LIN28 complex that could influence levels of OCT4. Our results strongly suggest that L1TD1 has an important role in the regulation of stemness.

Filia Is an ESC-Specific Regulator of DNA Damage Response and Safeguards Genomic Stability

“…Immunoblotting and immunofluorescent staining were performed according to the standard procedures (Narva et al, 2012). The primary antibodies were listed in Table S1.…”

The biology of DHX9 and its potential as a therapeutic target

“…In humans, DHX9 interacts with the LIM homeodomain transcription factor LMX1B, which is essential in mesodiencephalic dopaminergic neuron development [84]. DHX9 also interacts with the stem cell-specific RNA-binding protein L1TD1, which forms a complex with Lin28 to regulate translation of the stem cell factor Oct4, thus suggesting a role for DHX9 in human embryonic stem cell renewal [85]. Hence, the current evidence indicates that DHX9 is essential to development in a number of organisms.…”

“…It is thought that once recruited to Lin28 target mRNAs, DHX9 may aid in resolving inhibitory secondary structures. Further support for a role in Lin28-mediated translation regulation is provided by evidence that DHX9 also interacts with L1TD1, which forms a complex with Lin28 to regulate Oct4 translation in human embryonic stem cells [85]. …”

RNA-binding proteins in pluripotency, differentiation, and reprogramming

“…In the cytoplasm of hESCs, Lin28 interacts with L1td1 in P-bodies, a subcellular compartment where RNAs are directed either for translation or for silencing through miRNAs (Närvä et al, 2012). L1td1 (or Ecat11) is another RBP whose expression is rapidly downregulated upon differentiation (Wong et al, 2011).…”

“…L1td1 (or Ecat11) is another RBP whose expression is rapidly downregulated upon differentiation (Wong et al, 2011). In contrast to mouse ESCs, L1td1 is required for maintenance of self-renewal in human ESCs (Iwabuchi et al, 2011; Närvä et al, 2012). Although its exact function alone, or together with Lin28 remains to be determined, L1td1’s association with proteins in P-bodies suggests a potential role in translational regulation.…”