PACRG (parkin coregulated) is a multifunctional protein with distinct roles in ciliary motility and cellular signaling. As a microtubule inner protein (MIP), PACRG is essential for motile cilia beating, forming part of dynein-decorated doublet microtubules in cilia axonemes 1. PACRG binds directly to microtubules and alpha/beta-tubulin heterodimers with high affinity, bundling microtubules and forming branched aggregates 2. Structurally, PACRG adopts a helical repeat fold and forms complexes with MEIG1, facilitating axoneme formation through dual tubulin interactions 3. Beyond its ciliary functions, PACRG plays a protective role in cellular stress responses by suppressing cell death induced by unfolded proteins and facilitating inclusion body formation when proteasome function is inhibited 4. The protein also promotes TNF-induced NF-κB activation by interacting with the linear ubiquitin chain assembly complex (LUBAC), functionally replacing SHARPIN in this pathway 5. PACRG shares a bidirectional promoter with parkin and is co-regulated with it 6. Like parkin, PACRG is regulated by the ubiquitin-proteasomal system and is found in pathological features of Parkinsonian diseases, including Lewy bodies, suggesting potential involvement in neurodegeneration 7.