Retinal degeneration protein 3 controls membrane guanylate cyclase activities in brain tissue

Abstract

The retinal degeneration protein RD3 is involved in regulatory processes of photoreceptor cells. Among its main functions is the inhibition of photoreceptor specific membrane guanylate cyclases during trafficking from the inner segment to their final destination in the outer segment. However, any physiological role of RD3 in non-retinal tissue is unsolved at present and specific protein targets outside of retinal tissue have not been identified so far. The family of membrane bound guanylate cyclases share a high homology of their amino acid sequences in their cytoplasmic domains. Therefore, we reasoned that membrane guanylate cyclases that are activated by natriuretic peptides are also regulated by RD3. We analyzed transcript levels of the rd3 gene and natriuretic peptide receptor genes Npr1 and Npr2 in the mouse retina, cerebellum, hippocampus, neocortex, and the olfactory bulb during development from the embryonic to the postnatal stage at P60. The rd3 gene showed a lower expression level than Npr1 and Npr2 (encoding for GC-A and GC-B, respectively) in all tested brain tissues, but was at least one order of magnitude higher in the retina. RD3 and natriuretic peptide receptor GCs co-express in the retina and brain tissue leading to functional tests. We expressed GC-A and GC-B in HEK293T cells and measured the inhibition of GCs by RD3 after activation by natriuretic peptides yielding inhibitory constants around 25 nM. Furthermore, endogenous GCs in astrocytes were inhibited by RD3 to a similar extent. We here show for the first time that RD3 can inhibit two hormone-stimulated GCs, namely GC-A and GC-B indicating a new regulatory feature of these hormone receptors.

Retinal degeneration protein 3 mutants are associated with cell-cycle arrest and apoptosis

“…We interpret this result as indicating that the effect of RD3 on cell-cycle control is specific, because locations of the point mutations are at critical positions of the interface region interacting with guanylate cyclases [10], and any disturbance might weaken or diminish the impact of RD3 on cell cycle control. The interaction profile of RD3 is not restricted to photoreceptor guanylate cyclases, because we showed recently that the activity of natriuretic peptide receptor guanylate cyclases is controlled by RD3 in a fashion similar to photoreceptor cyclases [13]. These finding points to a more general role of RD3 in a signal transduction pathway involving a membrane bound guanylate cyclase.…”

“…The critical function of RD3 in health and disease apparently extend to non-retinal tissue, since recent investigations in human and mice tissues showed the expression of RD3 in different brain regions and in epithelial cells of various organs [12,13,14,15]. Loss of RD3 expression correlates with the progression of the pathogenesis in neuroblastoma and a poor survival prognosis [12,14].…”

“…This study tested whether RD3 can modulate the activities of non-sensory membrane bound guanylate cyclases GC-A and GC-B that are activated by natriuretic peptides ANP and CNP, respectively [13]. The active states of recombinant GC-A and GC-B and that of native GCs in astrocytes were inhibited by RD3 [13]. Collectively, these reports indicate that RD3 expression and function is not restricted to retinal tissue.…”

“…In addition to its high expression in the retina, RD3 is expressed in other organs and tissues, including the brain at both the transcriptional and translational level, but at a significantly lower level than in the retina [12,13]. A more recent study compared the expression of RD3 in astrocytes and neurones with those in the retina.…”

“…A more recent study compared the expression of RD3 in astrocytes and neurones with those in the retina. This study tested whether RD3 can modulate the activities of non-sensory membrane bound guanylate cyclases GC-A and GC-B that are activated by natriuretic peptides ANP and CNP, respectively [13]. The active states of recombinant GC-A and GC-B and that of native GCs in astrocytes were inhibited by RD3 [13].…”