  We investigate the simultaneous evolution of dust and gas density profiles at
a radial pressure bump located in a protoplanetary disk. If dust particles are
treated as test particles, a radial pressure bump traps dust particles that
drift radially inward. As the dust particles become more concentrated at the
gas pressure bump, however, the drag force from dust to gas (back-reaction),
which is ignored in a test-particle approach, deforms the pressure bump. We
find that the pressure bump is completely deformed by the back-reaction when
the dust-to-gas mass ratio reaches $\sim 1$ for a slower bump restoration. The
direct gravitational instability of dust particles is inhibited by the bump
destruction. In the dust-enriched region, the radial pressure support becomes
$\sim 10-100$ times lower than the global value set initially. Although the
pressure bump is a favorable place for streaming instability (SI), the
flattened pressure gradient inhibits SI from forming large particle clumps
corresponding to $100-1000$ km sized bodies, which has been previously
proposed. If SI occurs there, the dust clumps formed would be $10-100$ times
smaller, that is, of about $1 - 100$ km.
