The CK1 conference that just took place in Masaryk University in Brno is a great reason to dive a little bit deeper into the CK1 world. So why are these slightly overlooked kinases now gaining attention?

Let's start with the high-level picture. Kinases are fundamentally important enzymes involved in nearly every physiological process and naturally in plenty of diseases. Over the past few years, kinase inhibitor profiling has become an indispensable part of modern drug discovery research and it represents an engaging area for a broad range of biologists, biochemists and other researchers.

The inhibitor profiling of CK1s (casein kinase 1) is no exception (and it is also our newest target for DIANA Inhibitor Profiling). Historically (maybe) underappreciated, CK1 isoforms have recently emerged as key regulators of diverse cellular pathways and high-potential therapeutic targets, particularly in cancer biology, neurodegeneration, and chronobiology.

We won't make this longer than necessary, so let's see what we are going to explore!

CK1: What are they?
Cancer, neurodegeneration and other diseases
What inhibitors are used so far and how?
CK1 Inhibitor Profiling

What Is Casein Kinase 1?

Casein Kinase 1 (CK1) refers to a family of serine/threonine protein kinases conserved across eukaryotes. The "Casein" in their name dates back to the early discovery of this enzyme family's activity in phosphorylating casein, a milk protein, in vitro. However, this name is now considered misleading, especially because casein is not a physiological substrate in vivo and it has been showed that CK1s can phosphorylate other substrates (Tau, PER2, β-catenin, and others). In humans, the major isoforms include:

CK1α (CSNK1A1) and CK1 αL (CSNK1A1L)

CK1δ (CSNK1D) and CK1ε (CSNK1E)

CK1γ1, γ2, γ3 (CSNK1G1–3)

These isoforms differ in sequence homology, substrate specificity, subcellular localization, and regulatory behavior, yet share a highly conserved catalytic core. They also share a key regulatory pathway and that is the Wnt/β-catenin signaling, which is the ultimate mechanism for embryogenesis and cell proliferation.

CK1s are unusual among kinases: they are often constitutively active, lacking classical upstream activation, and instead regulated through autoinhibitory C-terminal domains, autophosphorylation, and protein-protein interactions. Their ability to act on primed substrates, requiring prior phosphorylation, adds an extra layer of regulation and contextual specificity.

From DNA Damage to Circadian Control: CK1s in Cellular Networks

CK1s integrate into many signaling hubs and as we already said the Wnt/β-catenin pathway is shared with all of them. But there are other important cell processes, that are influenced or regulated:

Circadian rhythm control (CK1δ/ε): Phosphorylation of PER1/2 regulates nuclear localization and degradation, tuning the ~24-hour cycle.

Wnt/β-catenin signaling: All of the CK1s are engaged in the Wnt/β-catenin signaling. CK1α is known as a key negative regulator. Other CK1s are positive regulators.

DNA damage and replication stress responses (CK1α, CK1δ, CK1ε): Regulates p53, Mdm2, and checkpoint kinases.

Endocytosis and vesicle trafficking (CK1γ): Modulates Dvl, clathrin adaptor proteins, and membrane-bound receptors.

Isoform-specific localization plays a critical role. Usually it differs between nucleus, cytosol and plasm membrane. This compartmentalization drives specificity in substrate recognition and functional output:

CK1α is often nuclear and chromatin-associated. It phosphorylates p53 and MDM2 in the nucleus, modulating DNA damage responses and apoptosis.

CK1δ/ε shuttle between cytoplasm and nucleus. They regulate circadian rhythms by phosphorylating PER2 in the cytoplasm before nuclear entry, controlling its stability and degradation.

CK1γs are membrane-anchored via C-terminal lipidation. CK1γ1 phosphorylates LRP6 and Dvl at the plasma membrane, modulating Wnt/β-catenin signaling.

CK1s in Human Disease: A Rapidly Expanding Landscape

It is typical that the kinases are involved in almost every process in the human body. CK1s are no exception. The outcome? Their dysregulation contributes to a growing list of diseases from cancer to FASPS:

Cancer

CK1α plays paradoxical roles: promoting β-catenin degradation (tumor-suppressive) but also inhibiting p53 and activating NF-κB (tumor-promoting).

CK1α loss is synthetically lethal in TP53-mutant leukemia, and is being targeted using degraders or allosteric modulators.

CK1δ is implicated in triple-negative breast cancer, lymphoma, and melanoma, often associated with MYC-driven transcription and proliferation.

Neurodegeneration

CK1δ/ε phosphorylate key aggregation-prone proteins: Tau (MAPT) in Alzheimer’s disease TDP-43 in ALS and frontotemporal dementia α-Synuclein in Parkinson’s disease

These phosphorylation events contribute to mislocalization, aggregation, and loss of function resulting in driving pathogenesis.

Circadian Disorders

Familial Advanced Sleep Phase Syndrome (FASPS): Rare hereditary circadian rhythm disorder in which individuals fall asleep and wake up several hours earlier than normal. It’s linked to mutations in CK1δ or its substrate PER2, affecting the stability and turnover of core clock proteins.

CK1ε variants have been linked to mood disorders and chronotype differences in human populations.

Viral Infections

CK1 is hijacked by viruses (e.g., SARS-CoV-2, HIV, HBV) to modulate host immune responses and phosphorylate viral proteins, affecting replication and immune evasion.

What Inhibitors Are Used So Far and How?

Several tool compounds and experimental inhibitors have been developed to target CK1 isoforms, though most lack robust isoform specificity and have off-target effects. Below are some notable examples: