Angeliki Ditsiou

Lemur tail kinase 3 (LMTK3) is an oncogenic Ser/Thr kinase implicated in breast cancer (BC) progression, therapy resistance, and poor clinical outcomes, yet the molecular mechanisms governing its regulation remain poorly understood, particularly the role of its C-terminal intrinsically disordered region (IDR). Given that IDRs frequently harbour hidden structural motifs that control protein dynamics, we combined computational, biophysical, and biochemical approaches to systematically map regulatory elements within the LMTK3 C-terminus, identifying two regions (residues 688–1095 and 1181–1486) that interact with the LMTK3 kinase domain (LMTK3-KD). Characterisation of these interactions revealed that LMTK3^1181–1486 displays preferential binding to inactive wild-type LMTK3-KD over a constitutively active mutant (LMTK3-KD^L313R), a behaviour consistent with a potential autoinhibitory interaction. Guided by AlphaFold3 modelling, we localised this interaction primarily to a short α-helical motif (α-helix 2; residues 1247–1258) within the C-terminal IDR and subsequently identified Ser1258 within this motif as a candidate regulatory phosphorylation site, using [γ-³²P]-ATP kinase assays and mass spectrometry. Phosphorylation at Ser1258 altered interactions between α-helix 2 and the kinase domain, reducing binding to wild-type LMTK3-KD while increasing affinity for LMTK3-KD^L313R. Functionally, phospho-null mutation of Ser1258 impaired oestrogen receptor alpha (ERα) upregulation, proliferation, migration, and clonogenicity in ER-positive BC cell lines, and reduced tumour growth in female BALB/c nude mice bearing orthotopic MCF7 xenografts. Together, these findings identify a previously uncharacterised regulatory element within the LMTK3 C-terminus and support a model in which Ser1258 phosphorylation modulates kinase domain interactions and LMTK3-driven oncogenic functions in BC.

Neuroendocrine tumors (NETs) represent a diverse group of neoplasms originating from neuroendocrine cells, presenting varied clinical behaviors and posing significant challenges in management. This review explores the emerging roles of receptor tyrosine kinases (RTKs) in the pathogenesis and progression of NETs, including vascular endothelial growth factor receptors (VEGFRs), insulin-like growth factor receptors (IGF-1R), RET, epidermal growth factor receptor (EGFR), and ALK. The dysregulation of RTK signaling pathways contributes to key cellular processes such as proliferation, survival, and invasion in NETs. We discuss the potential of targeting RTKs as therapeutic strategies in NETs, with a focus on recent developments in RET inhibitors and the therapeutic implications of RTK alterations.

Recently, the oncogenic role of lemur tyrosine kinase 3 (LMTK3) has been well established in different tumor types, highlighting it as a viable therapeutic target. In the present study, using in vitro and cell-based assays coupled with biophysical analyses, we identify a highly selective small molecule LMTK3 inhibitor, namely C36. Biochemical/biophysical and cellular studies revealed that C36 displays a high in vitro selectivity profile and provides notable therapeutic effect when tested in the National Cancer Institute (NCI)-60 cancer cell line panel. We also report the binding affinity between LMTK3 and C36 as demonstrated via microscale thermophoresis (MST). In addition, C36 exhibits a mixed-type inhibition against LMTK3, consistent with the inhibitor overlapping with both the adenosine 5′-triphosphate (ATP)- and substrate-binding sites. Treatment of different breast cancer cell lines with C36 led to decreased proliferation and increased apoptosis, further reinforcing the prospective value of LMTK3 inhibitors for cancer therapy.

In the last decade, LMTK3 (lemur tyrosine kinase 3) has emerged as an important player in breast cancer, contributing to the advancement of disease and the acquisition of resistance to therapy through a strikingly complex set of mechanisms. Although the knowledge of its physiological function is largely limited to receptor trafficking in neurons, there is mounting evidence that LMTK3 promotes oncogenesis in a wide variety of cancers. Recent studies have broadened our understanding of LMTK3 and demonstrated its importance in numerous signalling pathways, culminating in the identification of a potent and selective LMTK3 inhibitor. Here, we review the roles of LMTK3 in health and disease and discuss how this research may be used to develop novel therapeutics to advance cancer treatment.

The structure of oncogenic LMTK3 determines its role and functions allowing drug inhibition as a new therapeutic strategy.

As there is growing evidence for the tumor microenvironment’s role in tumorigenesis, we investigated the role of fibroblast-expressed kinases in triple-negative breast cancer (TNBC). Using a high-throughput kinome screen combined with 3D invasion assays, we identified fibroblast-expressed PIK3Cδ (f-PIK3Cδ) as a key regulator of cancer progression. Although PIK3Cδ was expressed in primary fibroblasts derived from TNBC patients, it was barely detectable in breast cancer (BC) cell lines. Genetic and pharmacological gain- and loss-of-function experiments verified the contribution of f-PIK3Cδ in TNBC cell invasion. Integrated secretomics and transcriptomics analyses revealed a paracrine mechanism via which f-PIK3Cδ confers its protumorigenic effects. Inhibition of f-PIK3Cδ promoted the secretion of factors, including PLGF and BDNF, that led to upregulation of NR4A1 in TNBC cells, where it acts as a tumor suppressor. Inhibition of PIK3Cδ in an orthotopic BC mouse model reduced tumor growth only after inoculation with fibroblasts, indicating a role of f-PIK3Cδ in cancer progression. Similar results were observed in the MMTV-PyMT transgenic BC mouse model, along with a decrease in tumor metastasis, emphasizing the potential immune-independent effects of PIK3Cδ inhibition. Finally, analysis of BC patient cohorts and TCGA data sets identified f-PIK3Cδ (protein and mRNA levels) as an independent prognostic factor for overall and disease-free survival, highlighting it as a therapeutic target for TNBC.