# Targeted degradation of MK2 is insufficient to block inflammatory cytokine production in human cells due to cooperativity with MK3 and MK5

## TL;DR

Targeting MK2 alone doesn't block inflammation because MK3 and MK5 help it, so multiple kinases need to be blocked for effective treatment.

## Contribution

Shows that targeting MK2 alone is insufficient due to functional redundancy with MK3 and MK5 in inflammatory signaling.

## Key findings

- Specific degradation of MK2 only partially reduces TNFα production in human PBMCs.
- Combined degradation of MK2/3/5 fully blocks TNFα production in human PBMCs.
- Genetic deletion of multiple MKs (MK2, MK3, MK5) significantly reduces inflammation more than single deletions.

## Abstract

Multiple p38 MAP kinase inhibitors have been developed for the treatment of inflammatory diseases such as rheumatoid arthritis, but their effectiveness has been limited due to toxicity and tachyphylaxis, leading to a lack of clinical benefit. Efforts have been made to circumvent this limitation by targeting individual substrates downstream of p38, including MK2 and MK5. This approach has failed to yield clinical benefit despite preclinical evidence of a therapeutic effect. We hypothesized that there is redundancy in the MAPK activating kinase family that would necessitate blocking multiple kinases to sufficiently impact inflammatory processes. We used heterobifunctional protein degraders that either specifically degraded MK2 selectively or degraded MK2/3/5 simultaneously to test the hypothesis, in addition to genetic approaches to enable knockdown. In human PBMCs, elimination of MK2/3/5 with heterobifunctional degraders resulted in full reduction of TLR4 or TLR7/8 induced TNFα, whereas MK2-specific degradation only attenuated TNFα biosynthesis. In contrast, both specific MK2 degradation and broad MK2/3/5 degradation inhibited TGF-β-induced collagen production in human fibroblasts. This observation was consistent with genetic deletions of MK2, MK3 and MK5 (singly and in combination) whereby single deletion of MK2, MK3 or MK5 attenuated lipopolysaccharide (LPS) induced TNFα production and had no effect on R848-induced TNFα production. Double deletion of MK2 and MK3 or MK2 and MK5 or MK2/3/5 triple deletion had a significantly greater effect on TNFα production regardless of stimulus. The combined data suggest cooperativity between MK2 and either MK3 or MK5 for efficient, cell context-dependent modulation of inflammatory responses.

Text and diagram illustrating the redundancy in the MAPKAP kinase family. It explains that therapies targeting MK2 alone are ineffective and highlights the need for blocking multiple kinases (MK2, MK3, MK5) for effective inflammatory response modulation. The diagram shows TLR stimulation leading to TNFα production under different kinase degradation conditions. Concludes cooperativity between MK2 and either MK3 or MK5 is essential for modulation.