Table 1 Class I-VII of the HLH transcription factors
From: The Id-protein family in developmental and cancer-associated pathways
Class | Structural domain | Representative members | Properties and function |
|---|---|---|---|
I | bHLH | E-protein family (E12, E47, E2-2/TCF-4/ITF-2, HEB) [1–3, 333] | Broadly expressed; Self- or heteroassociation with class II proteins; Regulation of neuro-, myo-, lymphogenesis |
II | bHLH | Myogenic regulatory factors (MyoD, myogenin, Mrf4, Myf-5,6) [6]; NeuroD/Beta2 [334]; Mash-1 [335, 336], d/e-HAND [337]; Twist [338] | Tissue-specific; Heteroassociation with class I proteins; Regulation of myogenesis (myogenic regulatory factors), islet cells differentiation (NeuroD/Beta2), neurogenesis (Mash-1), cardiac morphogenesis (d/e-HAND), and mesoderm development (Twist) |
III | bHLH-LZ | Melanocytes maturation (MiTF), B cells activation (TFE3), placental vascularization (TFEB), osteoclast development (MiTF, TFE3, TFEC), cell proliferation/differentiation, oncogenesis and apoptosis (Myc) | |
IV | bHLH-LZ | Homodimerization or heterodimerization with Myc; Regulation of cell proliferation | |
V | HLH | Heterodimerization with class I and, to a minor extent, class II proteins; Regulation of cell proliferation/differentiation during development and in cancer | |
VI | b(Pro)HLH | HES family (HES1-7) [13] | Regulation of cell proliferation/differentiation during embryogenesis |
VII | bHLH-PAS | AhR, HIFα, SIM, ARNT [12] | Regulation of xenobiotic (AhR/ARNT) and hypoxic (HIFα/ARNT) response genes, and of neural development (SIM/ARNT) |