Two-Step Coimmunoprecipitation (TIP) Enables Efficient and Highly Selective Isolation of Native Protein Complexes

Coimmunoprecipitation (co-IP) is one of the most frequently used techniques to study protein-protein (PPIs) or protein-nucleic acid interactions (PNIs). However, the presence of coprecipitated contaminants is a well-recognized issue associated with single-step co-IPs. To overcome this limitation, we developed the two-step co-IP (TIP) strategy that enables sequential coimmunoprecipitations of endogenous protein complexes. TIP can be performed with a broad range of mono- and polyclonal antibodies targeting a single protein or different components of a given complex. TIP results in a highly selective enrichment of protein complexes and thus outperforms single-step co-IPs for downstream applications such as mass spectrometry for the identification of PPIs and quantitative PCR for the analysis of PNIs. We benchmarked TIP for the identification of CD95/FAS-interacting proteins in primary human CD4⁺ T cells, which recapitulated all major known interactors, but also enabled the proteomics discovery of PPM1G and IPO7 as new interaction partners. For its feasibility and high performance, we propose TIP as an advanced tool for the isolation of highly purified protein-protein and protein-nucleic acid complexes under native expression conditions.

Remodelling of the nuclear lamina during human cytomegalovirus infection: role of the viral proteins pUL50 and pUL53

A fundamental step in the efficient production of human cytomegalovirus (HCMV) progeny is viral egress from the nucleus to the cytoplasm of infected cells. In the family Herpesviridae, this process involves alteration of nuclear lamina components by two highly conserved proteins, whose homologues in HCMV are named pUL50 and pUL53. This study showed that HCMV infection induced the mislocalization of nuclear lamins and that pUL50 and pUL53 play a role in this event. At late stages of infection, both lamin A/C and lamin B showed an irregular distribution on the nuclear rim, coincident with areas of pUL53 accumulation. No variations in the total amount of nuclear lamins could be detected, supporting the view that HCMV induces a qualitative, rather than a quantitative, alteration of these cellular components, as has been suggested previously for other herpesviruses. Interestingly, pUL53, in the absence of other viral products, localized diffusely in the nucleus, whilst the co-expression and interaction of pUL53 with its partner, pUL50, restored its nuclear rim localization in distinct patches, thus indicating that pUL50 is sufficient to induce the localization of pUL53 observed during virus infection. Importantly, analysis of the nuclear lamina in the presence of pUL50-pUL53 complexes at the nuclear boundary and in the absence of other viral products showed that the two viral proteins were sufficient to promote alterations of lamins, strongly resembling those observed during HCMV infection. These results suggest that pUL50 and pUL53 may play an important role in the exit of virions from the nucleus by inducing structural modifications of the nuclear lamina.

[Treatment of post kidney transplantation erythrocytosis (PTE) with ACE inhibitors]

BACKGROUND

Post kidney transplantation erythrocytosis is a frequent complication in male subjects. in our experience, it occurs in approximately 20% of transplant patients recciving cyclosporine inununosuppression therapy.

METHODS

Twenty-two patients with post kidney transplantation erythrocytosis were treated using ACE-inhibitors (lisinopril) at a dose of 2-5-5 mg/day for a mean period of 15 months. Owing to tbe onset of collateral effects, 27% of these patients requested the conversion of ACE into angiotensin II receptor antagonists (AII). Twenty out of 22 patients were male (90%).

RESULTS

Treatment resulted in a 15% reduction of hematocrit values compared to basal levels, which remained stable over time. No collateral effects were recorded, either for the kidneys or in terms of hypotension.

CONCLUSIONS

ACE-inhibitors (lisinopril) or alternatively the use of angiotensin II receptor antagonists, like Iosartan at low doses, is an effective and safe treatment for patients developing post-transplantation erythrocytosis (PTE).

[Treatment of post kidney transplantation erythrocytosis (PTE) with ACE inhibitors]

BACKGROUND

Post kidney transplantation erythrocytosis is a frequent complication in male subjects. In our experience, it occurs in approximately 20% of transplant patients receiving cyclosporine immunosuppression therapy.

METHODS

Twenty-two patients with post kidney transplantation erythrocytosis were treated using ACE-inhibitors (lisinopril) at a dose of 2-5-5 mg/day for a mean period of 15 months. Owing to the onset of collateral effects, 27% of these patients requested the conversion of ACE into angiotensin II receptor antagonists (AII). Twenty out of 22 patients were male (90%).

RESULTS

Treatment resulted in a 15% reduction of hematocrit values compared to basal levels, which remained stable over time. No collateral effects were recorded, either for the kidneys or in terms of hypotension.

CONCLUSIONS

ACE-inhibitors (lisinopril) or alternatively the use of angiotensin II receptor antagonists, like Losartan, at low doses, is an effective and safe treatment for patients developing post-transplantation erythrocytosis (PTE).